Lamps are special versions of SOLIDWORKS parts or Rhino blocks that have all of LTI Optics' detailed lamp model data incorporated in them. This means that when you run a raytrace you're using the full detailed lamp model, even if the display geometry is simplified. You will have accurate far and near field distribution, as well as full color data for our new color lamps. Rhino displays the exact 3D lamp model data. In SOLIDWORKS, there are two basic types of lamps you'll encounter.

Types

Full Rhino

Rhino will show the full Photopa lamp geometry, including emission surfaces. This is the actual geometry that is sent to the raytracer, and thus is polygon based.

Full SOLIDWORKS

For new lamps and popular old lamps, we'll have a full SOLIDWORKS part that shows the geometry of the lamp. This geometry is just for illustration, we use much more detailed geometry during the raytrace.

Generic Placeholder Geometry

For older lamps we'll have a simple placeholder part so that you know where the lamp is, but you won't see detailed geometry. Don't worry, we still use the detailed geometry in the raytrace, we just don't have a SOLIDWORKS representation of it.

For these lamps, the Lamp center is set at the 0,0,0 point from Photopia, which is generally the Photometric Center or center of the luminous area of the lamp. This is typically:

• Top center of the phosphor area for LEDs
• Arc center for MH lamps
• Center of tube for linear lamps

Adding A Lamp

Updating A Lamp

Using an IES file for a lamp

If your luminaire uses LEDs with off the shelf secondary optics from companies such as Ledil, Carclo, Fraen, etc. they may be represented using a special set of lamp models in Photopia's library. The special lamp models consist of planar geometry and will emit light in a distribution driven by the IES file you assign to it. The light will be emitted uniformly from the front surface of the lamp geometry. We have created a range of models that can be used for various sized optics. You will see them in the lamp list with names that begin with "LEDLENS..." The rest of the name indicates the geometry of the source, with a single number indicating a diameter. Some of these lamp models also include several copies so you can work with multiple lens types in the same luminaire. In this case, the extra copies have numbers at the end of their name. Some of these models include:

• LEDLENS20MM (This has a round emission area)
• LEDLENS50MM (This has a round emission area)
• LEDLENS75MM (This has a round emission area)
• LEDLENS19x95MM (This has a rectangular emission area for symmetric beams. It is sized for the Ledil Florence product line.)
• LEDLENS95x19MM (This has a rectangular emission area for asymmetric beams where the main throw is perpendicular to the long axis of the lens. It is sized for the Ledil Florence product line.)

SOLIDWORKS

To set the lamp model's IES file, just rename your IES file to match the model name you want to use and put it into the following folder: C:\ProgramData\LTI Optics\Library\Lamps

Note that this folder is sometimes hidden by Windows, so if you don't see it in Windows Explorer then change your Folder Options to display all hidden folders and files.

Once you load the lamp into your model, then you will set its lumens, LED watts and driver watts in the lamp properties screen to define the values appropriate for your LED, its running current, temperature and lens efficiency.

To update the IES file for your simulation, just update the IES file in the folder and re-run your simulation. The raytrace will use the latest data in the Library folder at the time you begin the raytrace.

Rhino

There are 2 ways to assign your IES file to a lamp model in Rhino. The first is to rename your IES file and copy it into the lamp library folder as described under Solidworks. The other option is to assign the IES file via the “Lamps editor” panel. If this panel is not already available, then you can open it by clicking on the gear icon in the upper right corner of a current docked panel and choose “Lamps editor [photopia]” from the list displayed. Select the LEDLENS… lamp model in the CAD view and then click the icon circled below in the Distribution section of the Lamps editor panel to browse to your IES file.

Once a lamp is loaded into Photopia, its IES file data is loaded into the model. The IES data is also loaded when the file is selected as described above. If you later need to change the IES file or if you’ve updated the data in the IES file, then reload the file via this import button.

LIMITATIONS

Light is emitted uniformly from the planar emission area, which is an approximation.

If you have lenses or reflectors close to the emission areas, they may not perform as they really will.

Using Rayset Data

Assigning a lamp to your Part geometrySOLIDWORKS Only

The following instructions describe how to create the solid part geometry for an existing Photopia lamp model.

1. Import or construct the geometry of your lamp model in a new SW part file. Note that most lamp manufacturers post STEP files for their parts on their websites. The lamp model part can be in any units as long as it is the correct size.
2. Move the lamp geometry so that it is centered around the part origin (0,0,0). Set up the geometry so that the center of the luminous area (the center of the chip faces for LEDs) is at 0,0,0. The geometry should be rotated so that the light emits toward the -Z direction and if you have a an array of LEDs along a PCB then orient its length along the Y axis. If you have a single emitter with geometry that isn't quadrilaterally symmetric, then load that LED into Photopia's standard CAD system and see how it is oriented with respect to Photopia's world coordinates and used that same orientation within SOLIDWORKS.
3. Add a reference coordinate system and name it "Lamp orientation." This should be added at the origin of the part and match the part's XYZ axes. Do not mate this coordinate system to anything and it will insert at (0,0,0) by default.
4. Set the name of the part to match the lamp model LDF file name. Note that lamp models that include reflective and/or refractive components, such as the dome lens on the Cree XM-L, will have a name that has "Core" added to what is shown in the Lamps.xls file. You can confirm the lamp model LDF name by loading the lamp in Photopia. The name will be shown in the LAMP layers and also as the text on the lamp axis layer.
5. With the reference coordinate system selected, choose Add Lamp from the Photopia menu and pick the lamp model you are creating from the list to get that lamp's attributes added to this part.
6. Save the part with a name that matches the lamp model LDF file name.
7. Add this part file the following folder: C:\ProgramData\LTI Optics\SolidWorks\Library\Lamps
8. Next time you add this lamp to a project you should see your new geometry.

Photopia models a wide range of material optical properties for various types of optical surfaces. The 3 general types of materials include:

Reflective - Materials that only reflect light. The reflected light can be specular, scattered or a combination, with properties varying by the light incidence angle. Reflectance properties can be defined as constant for all wavelengths or variable by wavelength. The wavelength range can be defined anywhere within the UV, visible or IR range.

Transmissive - Materials that both reflect and transmit light. The same properties defined for reflective materials can also be defined for transmitted light. Transmitted light can pass straight through a surface as a “specular” component, scatter or a have combination of both specular and scattered components. Transmissive materials are generally used to model light through diffusing lenses or lenses with repeated structured patterns such as prismatic lenses.

Refractive - Materials that model light via effects described by Snell's Law of Refraction and Fresnel's Equations. Thus, rays refract into and out of the material based on the indices of refraction of the outer and inner materials. Rays can totally internally reflect (TIR) inside of the material when incident upon the exit surface beyond the critical angle. Rays partially reflect/transmit at each optical interface based on Fresnel's Equations. Light is absorbed inside of refractors based on the material extinction coefficient. Refractive materials are generally considered to be clear (non-scattering) with smooth outer surfaces, but can include scattering properties on the outer surfaces as well as volumetric scattering from particles within the material.

Reflective and transmissive material properties are measured in our own optics lab with a custom-built HDR imaging based BSDF measurement device and custom-built integrating spheres. Spectral reflectance and transmittance properties can be measured from 200 - 1100nm. The light scattering properties (BSDF data) is measured at a wide range of light incidence angles for both isotropic and anisotropic materials. The total integrated reflectance & transmittance values are also measured over a wide range of light incidence angles.

All materials that include a wavelength range in their description have properties that vary by wavelength over the specified range. Such materials should only be used with light sources that emit within the same wavelength range. All materials without a wavelength range in their description have properties that are constant for all wavelengths in a simulation. Unless a specific wavelength is indicated in the material description, the material properties are generally appropriate over the visible range (380-780nm). Refractive materials for the visible range use a single index of refraction generally measured at the sodium D-lines, 589nm, which is very close to the center of the visible spectrum.

When using spectral materials, you need to use the "Power Distribution" raytrace option. This forces the raytracer to track spectral properties on each ray. This option is more memory & computationally intensive, so it isn't the default raytrace setting when the lamp flux energy units are set to lumens. The power distribution raytrace is not required for lumen based simulations since lamp spectral lamp properties within the visible can be represented with just 3 tristimulus values. Tristimulus values are all that's required since all color metrics can be derived from tristimulus values, including RGB display values, chromaticity values, color temperature, etc. Tristimulus values aren't sufficient for modeling dispersion, wavelength conversion with phosphors, computing photon flux, etc., so the power distribution mode is required for these types of simulations.

Assigning Materials

Lists of materials are provided within each CAD interface. You can also see a fully searchable material list that includes images for many of the materials.

Material spectral properties - Unless noted in the material description, the material properties are constant for all wavelengths. Materials with variable properties by wavelength include the wavelength range they cover at the end of their description.

SOLIDWORKS

The Photopia appearances are listed under the Photopia icon on the Task Pane on the right side of the screen. You can search the list by typing parts of a name or description in the box. You can filter the list by manufacturer or type. Selecting a material will show more details at the bottom of the pane.

There are several ways to assign appearances in SOLIDWORKS:

1. A selected appearance in the list can be dragged into the model and dropped onto the geometry to which it will be assigned. A flyout menu will pop up allowing you to assign the appearance to a face, feature, body, part, or part at the assembly level.
2. Pre-selecting a face, feature, body, or part in the FeatureManager and then double clicking on the Photopia appearance in the list will also assign the appearance.

Photopia for SOLIDWORKS uses the SOLIDWORKS Appearance system to assign Photopia raytrace materials to parts. This allows you to assign materials to individual faces, features, bodies or parts, and lets you use the Appearance Manager to audit which surfaces have Photopia Materials assigned as well as Display States to maintain several configurations of your material assignment.

Appearance Hierarchy

SOLIDWORKS geometry can have appearances assigned at multiple levels. For example, an appearance can be assigned to a part while a different appearance is assigned to a face on that part. In this case, the SOLIDWORKS appearance hierarchy will determine which appearance is used during the ray-trace. The same hierarchy is used for renderings in SOLIDWORKS. The order of the hierarchy is listed below. Levels higher in list supersede lower levels.

Controlling appearance order:

1. Component Level Assignment (part@assembly level)
2. Face Assignment
3. Feature Assignment
4. Body Assignment
5. Part Assignment

Rhino

The Photopia materials are listed in the Materials panel. You can search on any part of the manufacturer, designation, or description, choose a recently used material or scroll the general list. The “Value” shown indicates the reflectance (ρ), transmittance (τ) or index (n) for reflective, transmissive, or refractive materials, respectively. This is also your indication of the material type. The reflectance and transmittance values shown are for the 0° incidence angle only.

To assign a material to model geometry:

1. Select the geometry in the CAD view.
2. Find the material you want in the list.
3. Click the “Assign selected material” button or double click the material in the list.

Confirmation of the assignment will be shown at the bottom of this panel as well as on the command line.

Changing & Confirming Material Assignments

SOLIDWORKS

The Display Manager shows all appearance assignments in the model. Photopia appearance names are structured as “photopia + material filename.” The example below shows that the Photopia “Spec88” appearance is assigned to the “COB Reflector” part. To remove an appearance assignment, select the geometry in this tree view, then press the delete key. You can also reassign a new appearance to the same geometry to override the assignment.

Rhino

You can confirm the material assignment to geometry in Rhino by viewing the Photopia object settings in the Settings panel or by seeing what’s indicated in the Materials panel when the geometry is selected. Both panels provide a way to unassign the material or choose a new one.

Solid Model Transmissive Materials

Transmissive materials use measured BSDF data to drive the ray reactions. The measured BSDF data accounts for the effects of the full material thickness. The full reaction of the material is applied to a single ray/surface interface.

When a CAD model is constructed with solids, a lens will have a thickness and the ray will pass through multiple surfaces. Special Solid Model versions of transmissive materials have been created to avoid the full effect of the material being accounted for multiple times as the ray passes through the multiple surfaces. The Solid Model version of the material is indicated with (s) at the end of the material designation in the material list.

Transmissive materials that have unique properties for each side, such as smooth on one side and textured on the other, will have the “front side” surface indicated in the material description. The front side faces to the outside of solid model geometry. If your model requires the “back side” surface finish to face toward the incident light, then you’ll need to use the non-solid model version of the material, also referred to as the “double-sided” version. The double-sided version should only be assigned to single surfaces, not the entire solid model geometry. In SOLIDWORKS, this means assigning the double-sided material to the appropriate face of the solid part. In Rhino, it means first exploding any solid geometry to surfaces, then assigning the double-sided material to the appropriate surface.

Anisotropic Materials

Anisotropic materials are materials where there is a grain or feature that create a scattering distribution that is a function of the horizontal incidence angle. Ribbed aluminum, linear prisms and elliptical diffusers are a few examples of anisotropic materials.

In the library anisotropic materials are identified by a (A) in the name and the word "anisotropic" in their description.

Just like other materials, the first step is to assign the appearance/material to the geometry using the same steps outlined above.

The next step is to orient the material which depends on your version of Photopia.

Volumetric Scattering

Beginning with Photopia 2017, Photopia supports volumetric scattering refractive materials. This is for materials which scatter light within their volume, usually via pigment or diffusion particles. These are a special class of Refractive materials, and as such require the General Refractor Module or Photopia Premium. Volumetric scattering can also be used along with spectral material properties to model phosphor particles suspended in a clear material. With a volumetric scattering material, your geometry will impact the scattering (thicker parts will scatter more).

Photopia uses a specific XML formatted file for defining the material properties. For Volumetric Scattering, the scattering is described by the Beer-Lambert Law. Photopia accounts for the extinction coefficient within the clear base material, the scattering coefficient (likelihood to scatter), the absorption of the scatter reaction, as well as the distribution and energy conversion of the scatter reaction.

Current Library materials with Volumetric Scattering are:

• Evonik Acrylite LED EndLighten 0E011 L - for 12-24" wide sheets
• Evonik Acrylite LED EndLighten 0E012 XL - for 24-48" wide sheets
• Evonik Acrylite LED EndLighten 0E013 XXL - for 48-72" wide sheets
• Generic 3000K phosphor particle in liquid silicone
• Generic 3000K phosphor particle in acrylic
• OptiColor ACC1410WT 2.5% Loading Acrylic Diffuser
• OptiColor ACC1410WT 4.25% Loading Acrylic Diffuser
• OptiColor ACC1410WT 6% Loading Acrylic Diffuser
• OptiColor ACC2170WT 4% Loading Acrylic Diffuser
• OptiColor ACC2170WT 8% Loading Acrylic Diffuser
• OptiColor ACC2170WT 12% Loading Acrylic Diffuser
• OptiColor PCC2258WT 1% Loading Polycarbonate Diffuser
• OptiColor PCC2258WT 1.75% Loading Polycarbonate Diffuser
• OptiColor PCC2258WT 3% Loading Polycarbonate Diffuser
• OptiColor PCC2393WT 1.5% Loading Polycarbonate Diffuser
• OptiColor PCC2393WT 3.75% Loading Polycarbonate Diffuser
• OptiColor PCC2393WT 6% Loading Polycarbonate Diffuser

Full details are provided in this Volumetric Scattering Documentation.

Adding a Material to the Library

If you're looking for a material that you don't find in the Library, please let us know and we'll work on adding it. Often, you may use a custom material that isn't generally available. We can add this material to a custom library for your company. For information on getting a material in the Library, please see this order form.

Modifying a Material in the Library

You can modify the integrated reflectance of reflective materials, the integrated reflectance and transmittance of transmissive materials, and the index of refraction and extinction coefficient of refractive materials. The integrated reflectance and transmittance values can be changed as a function of incidence angle. You can also change the ratio of the specular component to the scattered light for both reflective and transmissive materials. You cannot edit the material BSDF data. The material file descriptions are as follows:

Reflective Material Files:

Filename.rfl - ASCII file of integrated reflectance values at each incidence angle. Files can contain an arbitrary angle set, so long as 0, 90 and 180 degrees are included. 0° is the front side of the material. Valid reflectance values range from 0.0 to 1.0.

Filename.brd - Binary file of the BRDF data for a material. This file cannot be modified. A .brd file only 2 bytes in size indicates the material is specular.

Filename.rsc - ASCII file specifying the ratio of the reflected light that is reflected in a specular manner. Note that these are not the specular reflectance values, but the fraction of the reflected light that is specular at each angle. To derive specular reflectance from these values, multiply these values by the reflectance at each incidence angle. Valid values range from 0.0 to 1.0. This file may or may not be associated with a material. A data byte indicating whether or not the material has a specular reflectance component is contained in the .brd file.

Transmissive Material Files (includes reflective files above, plus the following):

Filename.trn - ASCII file of integrated transmittance values at each incidence angle. Files can contain an arbitrary angle set, so long as 0, 90 and 180 degrees are included. Valid transmittance values range from 0.0 to 1.0.

Filename.btd - Binary file of the BTDF data for a material. This file cannot be modified. A .btd file only 2 bytes in size indicates the material is clear or image-preserving.

Filename.tsc - ASCII file specifying the ratio of the transmitted light that is transmitted in a straight-through manner. Note that these are not the straight-through transmittance values, but the fraction of the transmitted light that passes through un-scattered at each angle. To derive straight-through transmittance from these values, multiply these values by the transmittance at each incidence angle. Valid values range from 0.0 to 1.0. This file may or may not be associated with a material. A data byte indicating whether or not the material has a straight-through transmittance component is contained in the .btd file.

Refractive Materials Files:

Filename.rfc - ASCII file containing 3 values: the index of refraction of the outside medium (usually assumed to be air at 1.0), the index of refraction of the material averaged over the visible spectrum, and the extinction coefficient in units of inches. Note that the extinction coefficient is applied in the equation: Trans = e^(k*L), where e is the exponential (2.71), k is the extinction coefficient, and L is the distance the ray travels in the material in inches. Thus, k is a value per inch.

Spectral Material Files:

The spectral data for reflective & transmissive materials are defined in several different files. The .spdrfl & .spdtrn files include an incidence angle, multiplier and reference to a spectral matrix file (*.spdmatrix) on each line. The multiplier scales all values in the .spdmatrix file. The spectral reflectance & transmittance is defined in a matrix, where each row is an input wavelength, and each column is an output wavelength. For materials that don't shift wavelengths, all reflectance/transmittance values are shown for each wavelength along the diagonal of the matrix. All other values are 0. The first 3 values in the matrix file define the wavelength range as start, end, increment in nm. Wavelength increments can't be less than 1nm at this time.

The first 3 values in the .spdrfc refractor material files define the start, end and wavelength increment in nm. The remaining lines include the outside index, inside index and extinction coefficient for each wavelength.

Spectral materials also require a .material file.

To Modify Material Files:

You can modify any of the ASCII files described above with a text editor such as Notepad. Follow the instructions below to create a new version of a file without changing the original copy:

Photopia has 2 types of recorders that collect flux density onto surfaces, recording planes & recording objects.

Recording planes are flat, rectangular surfaces that only collect light incident onto one side. Since their geometry is limited to flat rectangles, their grid resolution can be defined, and all grid values are available to view in the results. Geometry used to define recording planes can't also be optically active as a reflector or lens surface.

• only planar rectangular surfaces
• are not optically active (must not have a Photopia material assigned)
• records incident energy on front only - 1 channel

Recording objects can be made for any reflector or lens optical surfaces in the model. Unlike recording planes, these surfaces can have any shape or curvature and must be optically active. The flux density is recorded on all mesh polygons of recording objects for incident and exitant light, for both the front and back sides of the object surfaces. So there are 4 sets of data (channels) for recording objects.

• any surface shape (not necessarily flat or planar)
• are optically active (must have a Photopia material assigned)
• records incident and exitant on front and back - 4 channels

Create Recording Planes

Modifying Recording Planes

Viewing Recorders

You can view recording planes & recording objects by choosing Results and then the Illuminance Planes / Recording Planes tab, or turning on their display in the Model view using the Recorder Display On/Off button.

Creating recording objects

recording objects allow you to view the light interacting with any object in your model. The object surfaces must be optically active, so they need to have a reflective, transmissive or refractive material assigned to them. If you don't want the object to impact the light in your model, you can assign the CLEAR001 transmissive material.

Recorder Display Settings

SOLIDWORKS

Rhino

Predefined Render Scripts: Render Script Presets allow you to select from a default set of display settings, including: false color, true color, grayscale, spectral shifts for non-visible wavelengths and Delta u'v' for color uniformity.

Render Script: Once a preset render script is selected, then the render script will be displayed in a separate box. All values of that render script can then be edited to manipulate the recorder display even further.

Global Max: By default, all recorders will be scaled to the global max value found on all recorders. The global max is automatically found when the "Global scale max" parameter is set to 0 in Rhino. You can enter any other value there if you prefer.

Legend: A legend is displayed when using global scaling and viewing gray scale or false color plots. If you uncheck the "Global scale enabled" box in Rhino or switch to local scaling in SW, then each recorder will be scaled according to its own max value. A legend can't be displayed in this case since the same colors will represent different magnitudes. When global scaling is used, the value of red on the legend is based on both the max value found on all recorders as well as the area over which that max is achieved. If the max is only on a very small area, indicating “noisy” results, then red will be assigned to a lower value to allow then colors of the legend to represent more of the data on the recorders. The true max value will be shown to the upper left of the legend display.

Global Recorder Smoothing: The "Global recorder smoothing" option determines whether or not the data on each patch is blended with neighboring patches. Smoothing the data makes a more realistic looking image of the light pattern. If you turn off the smoothing, then you see the raw data in each patch of the recorder.

Channel: This allows you to view any of 4 data sets on the surfaces. The channels are the incident light onto the front and back sides of the surfaces as well as the exitant (emitted) light from both the front and back sides. All 4 channels are available for recording objects, but only on the front incident light channel is available for recording planes.

False Color - Incident

Incident illuminance magnitude mapped to a typical false color scale.

True Color - Incident

Incident illuminance from a 4000K LED. Note some slight red in the area where the backrest and seat join from the interreflected light off the red panels.

True Color - Exitance

The true color exitance shows the color of light reflected off the seat which has slate gray and cherry red regions.

Delta u'v' from average: The "Delta u'v' from average" plot allows you to view quantitative color differences in the uniform u'v' color space. In this color space, a value of 0.001 is 1 MacAdam ellipse, which is a just perceptible color difference. Beam color uniformity requirements sometimes specify an allowable range in this color space, such as 0.004 or 4 MacAdam ellipses. In this plot, black is 0 and bright green is the highest delta u'v' value on the plane. This plot type supplements the true color plot when color differences in the light pattern are subtle, especially for tunable white lighting applications.

LED TIR Optic

TIR optic with pillow mixing features uses LED array with 7 2700K and 7 5000K LEDs.

True Color

Subtle color variations are seen around the beam perimeter.

Delta u'v'

This plot shows the quantitative color variation over the plane. Perimeter color variations are now very clearly identified.

Enable Recorder Display: The display of the individual recording planes and objects can be set in this section. Checked items are displayed when the recorder display in the CAD view is toggled on. This list is a function of the selected channel. Recording planes only include data for the “incident front” channel, so they will only be listed when this channel is selected.

You'll need to tell Photopia how to orient your Photometric Coordinate System before raytracing. You'll basically be defining what is 'up/down & forward/back, which should be the same orientation as the test. You can find more explanation of photometric conventions here.

SOLIDWORKS

You first need to create a Reference Coordinate System that defines the location and orientation of the “photometric coordinate system.” The -Z axis of this reference coordinate defines the 0-degree vertical angle and +Y defines the 0-degree horizontal angle in a Type C photometric coordinate system. The origin defines the photometric center. See more details in the sections below.

Select the reference coordinate system and then click the Photometric Settings button on the Photopia CommandManager. This will automatically mate the photometric coordinate system to the reference coordinate system. This will create a new virtual part in the assembly when this property management page is closed.

You can modify the orientation & location of the photometric coordinate system by modifying the properties of the reference coordinate system to which it is mated.

Rhino

Click the toolbar button for the Photometric Output Settings

You can visually confirm the location & orientation of the photometric coordinate system by clicking the Show/Hide Photometric Sphere icon on the Photopia toolbar.

Descriptions of all settings are provided in the sections below. A few that are specific to Rhino are provided here.

Photometric Nadir The direction of a vector toward the horizontal and vertical angles of 0 degrees. Generally, the direction of the beam center. This defaults to the world -Z axis.

Photometric Azimuth The direction of the 0-degree horizontal angle. This defaults to the world +Y axis.

Manufacturer If a value is provided, then this will be included as a keyword in the IES file.

Luminaire Description If a value is provided, then this will be included as a keyword in the IES file.

Catalog Number If a value is provided, then this will be included as a keyword in the IES file.

Report Type - This selection affects the default photometric coordinate system type as well as the default photometric report that shows relevant data for the various applications. A wider range of reports is available in the Reports view in SolidWorks and in Photopia Reports.

Photometry Type - The photometric coordinate system type defines the orientation and angle references of the spherical coordinate system. The appropriate type to use depends on your application. The diagrams below show the “direct” half of the photometric sphere and how it’s aligned with the reference XYZ coordinate system. This will be the “reference coordinate system” in SolidWorks and the world coordinate system in Rhino by default. The rings and ribs in the “photometric web” are defined by the horizontal and vertical angular resolutions. The shaded region shows the angles that will be included in the photometric report. The data is averaged within the hemisphere based on the beam symmetry. The photometric sphere preview shown in SolidWorks and Rhino is scaled to be similar in size to the model geometry. It is not shown at its actual size based on the specified test distance.

Type A

The standard coordinate system for automotive, aerospace, and marine lighting devices. Photometric requirements for devices in these industries define min and max intensity values at various angles in this coordinate system. The horizontal and vertical angles can be referred to as “X” & “Y”in some standards. The beam center is generally in the direction of travel and is oriented toward the 0X, 0Y (0H, 0V) directions.

This image shows horizontal angles of (-90(10)90) & vertical angles of (0(5)90). The specific angle sets selected depend on the angles at which required intensity values are defined. Certain report types that check for beam compliance with a standard will list the required angle sets. Horizontal angles can range from -180 to +180 degrees. Vertical angles can range from -90 to +90 degrees.

For aerospace applications where light can emit in all directions around a device, you will orient the +Z axis of the reference coordinate system in the aft direction and +Y toward the sky. The full range of horizontal and vertical angles should be used, generally H: (-180(5) 180), V: (-90(5)90).

Type B

The standard coordinate system for outdoor floodlights and sports lighting.

This image shows horizontal angles of (-90(5)90) & vertical angles of (0(5)90). Horizontal angles can range from -90 to +90 degrees. Vertical angles can range from -180 to +180 degrees, but most of these types of luminaires do not have any “indirect/back” light, so the vertical angles will range from -90 to +90 degrees.

Type C

The standard coordinate system for indoor and outdoor area & street lights for architectural lighting.

This image shows horizontal angles (designated as “L” for lateral) of (0(15)90) & vertical angles of (0(5)90). Horizontal angles are also sometimes represented by the Greek letter psi and referred as the “C plane” in Europe. Horizontal angles can range from 0 to 360 degrees. Vertical angles can range from 0 to 180 degrees. Vertical angle references include “V”, the Greek letters theta and gamma. “C-gamma” is the common European reference to the Type C coordinate system.

The angular resolution is specified between the start and end angles, e.g. (0(5)90) defines an angle set that starts at 0, increases in 5-degree increments, and ends at 90. The smaller the angular increment, the more rays you need to trace to resolve the increased resolution of the distribution. Use finer angular increments when the intensity distribution has narrow peaks or valleys. Use larger increments when the distribution is wider and smoother. In general, we recommend that the horizontal angular increment be kept at 15 degrees or less and the vertical increment at 5 degrees or less.

It’s best to use the minimum range of angles required to fully describe the beam, accounting for the beam symmetry. The angle sets will then indicate the type of luminaire distribution and you will get the smoothest intensity distribution with the fewest rays as Photopia will average data over the different quadrants. The vertical angle range options include:

• Direct: 0 to 90 degrees
• Indirect: 90 to 180 degrees
• Direct/Indirect: 0 to 180 degrees

There are 4 beam symmetry options for the horizontal angle range as shown in the next 2 images. These show the luminaire orientation with respect to the photometric coordinate system, with different conventions for quadrilateral symmetry in North America compared to the rest of the world. Bilaterally symmetric distributions should orient the strong side of the beam toward the 0-degree horizontal plane.

This screen allows you to modify the parameters that control all aspects of the raytrace process. The following sections provide a description of each of the parameters.

SOLIDWORKS

Rhino

Ray Count

Specifies the number of rays for the raytrace, emitted from all sources combined. The more rays that are traced, the more refined the results. The default of 2.5 million is generally sufficient for initial results.

Each component of the results will resolve at a different number of rays.

Below is the order in which items typically resolve.

1. Optical Efficiency (~50,000 rays)
2. Intensity Distribution (~2,500,000 rays with 5deg vertical angular resolution)
3. Recording Planes (~10 to 25 million rays at 100x100 grid size)
4. Color Difference (~100+ million rays)

Reaction Count

Specifies the number of ray reactions to trace. Each ray intersection with an optically active surface is a ray reaction. The default of 25 is generally sufficient for most light to emit from or diminish within an optical system. The “Reached interreflection limit” value in the “Anomalous interactions” section of the “Raytrace Report” indicates how much light was still interacting within the optical system due to this limit. It's generally best to set the reaction count high enough so that only a small percentage of the light reaches this limit. Light pipe/light guide designs or refractors with volumetric scattering particles generally require much higher values, such as 100+ ray reactions.

Lamp Flux Energy Units

The simulation can be run with the lamp output defined in lumens, radiant watts, photon flux or PAR photon flux. Lumens are appropriate for all lighting applications for which photometric output is required. Radiant watts provides radiometric output for applications such as optical sensors, UV curing and disinfection. Photon flux or PAR photon flux are most commonly used for horticulture applications. Both "Photon flux" and "PAR flux" are based on the lamp output in micro-mol photons per second. Photosynthetically Active Radiation (PAR) flux limits the results to only wavelengths between 400-700nm. Most horticulture applications require the use of PAR flux.

When you are using lamp models that include their full spectral details, then the lamp output can be defined in lumens, radiant watts, photon or PAR flux. They are all linked by the lamp SPD, so entering output in any of these units automatically updates all of the others. If you only know the lamp output in lumens based on the LED datasheet and power parameters for example, then you can enter the output in lumens even if you want results in PAR flux. Just be sure to set the lamp flux energy units in the raytrace settings as you require before the raytrace is run. Photopia does the proper conversion from radiant watts to photon flux at every wavelength of the SPD in the intensity distribution and on irradiance planes. So you can mix any combination of white and colored LEDs and get the right PAR flux values, for example. It is important that the SPD for the lamps you choose from Photopia's library match your actual LEDs if you will be relying on the right conversion from lumens or radiant watts to PAR flux. Entering your LED output in PAR flux directly avoids the need for an exact SPD match, but the LED output in PAR flux is not always provided on datasheets.

Ray Shadowing

Used for ray generation, this ensures that lamp parts which shadow the emission are taken into account. Leave checked for the most accurate results.

Minimum Ray Energy

If a ray's energy falls below this setting, it will no longer be traced through the system. This helps speed up a raytrace by reducing time spent on insignificant rays. The amount of light lost in the raytrace due to this limit is reported in the “Anomalous interactions” section of the “Raytrace Report.”

Exclude Reactions

Enabling this option allows you to remove any number of initial ray reactions from the output, starting with ray reaction 0. This allows you to isolate any part of the output by the ray reaction number to more clearly see “higher order” effects and help isolate their cause. For example, if you have a reflector design that emits both direct and reflected light, you can isolate the beam created from the reflector by removing the 0th ray reaction from the output. You enter the Exclude reactions through value, which would be 0 in this example. Note that some LED models include optically active components such as a primary lens, so in this case your “exclude through” number would need to be increased to account for the ray reactions within the LED package.

Update Frequency (seconds)

Specifies how often the output will be updated as the raytrace progresses. The analysis status view will show the # of rays and percent complete with each update.

Power Distribution Raytrace

This option enables the full spectral data to be tracked with each ray. This is the most general way of tracking ray properties, but results in a slower ray trace since more data is processed with every ray reaction. When running a lumen based simulation that does not use any materials with spectral properties, you can leave this option disabled and all spectral properties will be converted to tristimulus values. Thus only 3 extra parameters are tracked & processed on each ray, resulting in a faster ray raytrace with less memory and storage. Tristimulus values are all that's needed to compute all color metrics including the true color recorder images. If the lumen based simulation includes spectral materials, which are indicated with their spectral range shown in their description, then you need to enable the power distribution raytrace for those material properties to be used. For example, if you want an acrylic lens to use an index of refraction that changes by wavelength, then choose the ACRYLIC1 material with a description of “standard clear acrylic (250-2800nm)” and enable the power distribution option.

All radiant watt or photon flux simulations automatically enable the power distribution raytrace since their output requires the full spectral ray data.

When a power distribution raytrace is enabled, you can also specify the resolution in nm. A finer resolution might be needed for models that include narrow band features in their lamps and/or materials. The finer the resolution, the more data tracked on each ray, and thus the slower the raytrace and the larger the memory requirements.

Preserve Power Distribution Data

This option refers to the spectral power distribution data stored with recorders. When a power distribution raytrace is run, all spectral data can be stored for each patch of every recorder in the model. This data is needed if you will be using any of the render display scripts that remap the spectrum for visualization purposes. For example, if you plan to remap UV wavelengths into the visible range so that you can view the recorders in a way similar to true color displays, which show both color mixing and irradiance magnitude in the same display. Having the full spectral data available for such display options is helpful, but it also requires more memory. This is OK for a few recording planes at their default resolution, but can become a burden on system resources when you have large recording objects with hundreds of thousands of polygons, especially since recording objects store 4 channels of data for every polygon. So it's best to leave this option off unless you specifically need the spectral remapping feature for recorder display visualization.

Sample Ray Count

The number of rays that you want displayed in the CAD view. The default of 0 results in no displayed rays. When you do want to display rays, we recommend a fairly low number such as 500 so that you can more clearly see the general ray trends. Using too high a number fills the screen with so many lines that it can be difficult to see their interactions with the model geometry. You may need to use a higher number however, when filtering the rays to see how they react with specific optical components in the model.

Sample Ray Length

The length of the ray after its last interaction with any optical components in the model, including recording planes. This value can be changed after the raytrace in Rhino and the ray display will update.

Sample Ray Filtering

For each sample ray, Photopia keeps track of several properties of that ray, including the objects that it interacted with. This allows you to filter the sample rays to display only the rays that fit a specific criteria.

SOLIDWORKS

Click the Filter sample rays button on the Photopia CommandManager to open the following PropertyManagement page.

Show rays by object - Display rays that interact with all objects in the model or only those you select. Note, “farfield” is the far field photometric sphere. It’s listed as both a material and an object.

Show rays by material - Display rays that interact with all materials in the model or only those you select.

Range of reactions to filter - Defines the start and end ray reaction numbers to display.

Expert advanced ray filtering – - You can type a list of ray reaction numbers to show. The numbers do not need to be consecutive. Use a space between each value.

Invert filter - Inverts the current filter setting so all rays that were not being displayed are now displayed while the filtered rays are not.

Filtered Ray Color - Specify the filtered ray color in the box just after Invert filter. The red, greed & blue values are specified from 0 to 1, separated by spaces.

Rhino

Click the Sample Ray Settings button in the Photopia Settings panel to view the screen.

Sample ray color - Set the color of the unfiltered sample rays. To change the color, click on the color designation, then click the drop-down arrow in the cell and choose a color on the pop-up dialog.

Exceptional ray color - Set the color of exceptional rays. These are rays that were stopped in the raytrace due to the problems listed in the “Anomalous interactions” section of the “Raytrace Report.”

Filter enabled - Check this option to view the filtered rays as defined by the following settings. When unchecked, all sample rays are displayed.

Display exceptional rays - Check this option to display the exceptional rays.

Invert filter - Inverts the current filter setting so all rays that were not being displayed are now displayed while the filtered rays are not.

Filter from reaction - The start reaction number of the rays displayed.

Filter to reaction - The end reaction number of the rays displayed.

Filter color - Set the color of the filtered rays.

Object filters - Display rays that interact with all objects in the model or only those you select. Note, “farfield” is the far field photometric sphere. It’s listed as both a material and an object.

Material filters - Display rays that interact with all materials in the model or only those you select.

Saving Sample Rays as CAD Entities

SOLIDWORKS

The filtered rays can be saved to a 3D sketch in the assembly. If you want to save all rays to the sketch, then keep the default filter settings that show ray reactions with all objects & materials. When finished defining the filter settings, click the Save filtered rays to sketch and close button at the bottom of this PropertyManagement page. A new 3D sketch will be created to store the filtered rays. If you want to separate different sets of rays into different 3D sketches, then define a new filter and click the same button when closing this PropertyManagement page.

Rhino

Choose Photopia > Save 3D Rays from the main menu. This will save the 3D rays displayed with the current filter settings to the current layer. If you want to save different sets of rays to different layers, then change the filter settings and current layer as desired.

Mesh Resolution

The Photopia raytrace engine uses a meshed model for the raytrace. Rhino and Solidworks bodies are natively surfaces, not meshes, so they must be converted before raytracing. This conversion is handled automatically when you begin a raytrace, but you may need to override the default meshing for parts with fine details.

For smooth lenses or detailed geometry, we recommend using the Maximum Angle and set it to 1 or 0.5deg.

For recording objects, we recommend using the Maximum Element Size and Max/Min Edge Length to set a reasonable cell size.

SOLIDWORKS

In Solidworks, the default resolution will generally work well.

For any sensitive or small parts, the best approach is to create a Mesh Body from your Body (in Solidworks 2018 or newer).

Mesh Body

1. Open the Part file, or edit the Part within the assembly.
2. Choose Insert > Surface > Convert to Mesh Body ...
3. Select the Body to convert
4. Update the resoultion settings, we suggest setting the Maximum Angle Deviation and Maximum Element size.

5. Click check and you'll see the new mesh
6. Assign the Photopia Appearance to this Mesh Body.

For Solidworks 2017 or older, you can control the resoution to some degree using the Image Quality settings. This method cannot generate a mesh as high resoution as the Mesh Body approach.

Image Quality

1. This setting should be applied within a Part file.
2. Choose Tools > Options > Document Properties > Image Quality
3. Find the Shaded and draft quality HLR/HLV Resoultion section
4. Pull the slider into the red zone.

Rhino

In Rhino, click on the Photopia Mesh Settings.

You can adjust any of the parameters and then click Preview to see the mesh for your model.

Any setting kept at 0 will be non-controlling.

Maximum edge length and Maximum Angle are the two most useful settings.

See Rhino’s documentation ( https://docs.mcneel.com/rhino/7/help/en-us/documentproperties/mesh.htm ) for more details about these mesh parameters.

By default, these parameters will apply to all surfaces in your model that are assigned Photopia materials. This is indicated with the *custom Mesh Parameters setting in the Photopia Object Settings panel. Select one or more surfaces/objects to see this setting. If you require different mesh settings on some surfaces in your model, then choose another option from the drop-down list. Options with names such as “5mmX5mm” indicate mesh settings with minimum and maximum edge lengths set to 5mm. These “square” grid mesh options work well for object recorders, especially those with an extruded shape. Keep in mind however, that Rhino does not subdivide meshes along the extrusion direction of an “extrusion” entity. So if your surface was created with the extrusion tool, then Explode it first, so that it’s a “surface” entity.

Non-critical model geometry can be set to the “Coarse0.5” option, which creates a medium density mesh with Rhino’s Density setting to 0.5.

There is no preview option when assigning mesh settings to surfaces this way, so you can confirm the mesh appearance by using the PhotopiaExtractMesh command. Select a surface and then run this command. Its simulation mesh will be created and stored on the current layer. Once you’ve confirmed the mesh details, then select this mesh and delete it. The mesh will be created from the original surface when you start the raytrace.

Results can be viewed either in the SOLIDWORKS window, Rhino panel or in Photopia Reports. This allows you to view several outputs at the same time. To view results, click the Results button on the Solidworks CommandManager or click the Results panel in Rhino.

In Solidworks the results are saved per configuration, so a single assembly model can include the results for various design options.

A wide range of photometric, radiometric & colorimetric results are shown in specialized reports & plots. Reports are generally oriented toward specific industries, such as architectural lighting, automotive, aerospace, horticulture, disinfection, etc.

See our glossary for an explanation of specific types of results.

Intensity distribution data can be saved to standard IES & EULUMDAT file formats. In Solidworks, choose either of these file options in the left bar of the Results screen. Then click the export icon in the upper right corner of the screen. In Rhino, click the "IES/LDT" icon in the upper right corner of the Reports panel.

You can also view the Analysis Status during a raytrace.

The Parametric Optical Design Tools (PODT) create reflector and lens geometry based on how you want to control the light. The parameters for the various types of optics define both the physical size and aiming properties of the design. These tools are useful when you are designing a reflector or lens that needs to produce a particular beam pattern. The optical design tools allow you to define the range of angles over which the light is directed as well as how much light is directed toward each angle in the beam. Thus, they allow you to tailor the beam intensity distribution.

Reflector Design Tool Overview

The reflector design tools create reflector profiles based on aiming light toward a range of angles or toward a range of points. Using “aim by angle” creates a reflector built from a set of parabolic sections. Using “aim by point” creates a reflector built from a set of elliptical sections. As an example, consider a reflector that aims all light toward a single angle at the beam center, creating a very narrow beam pattern. This reflector is a single parabola that collimates light as shown below when revolved into a parabolic surface:

The aiming angle in the reflector above is toward the 0° vertical angle in the reflector's intensity distribution. Now consider changing the aiming angle to be 20° away from the beam center, as shown below. This is still a single parabolic profile, but the profile has been rotated by 20° about its focus. Revolving this profile about the beam central axis (a vertical line), results in the reflector shown below. Whereas the reflector aimed toward 0° would create a narrow beam intensity distribution, the reflector aimed at 20° would produce beam pattern with a spike 20° off center.

The parametric reflector design tools allow you to aim light toward any number of angles in your beam pattern, which results in a set of parabolic profiles all joined together. Combining 0 and 20 into a single reflector looks like this.

Simulating these 3 reflectors with an LED at the focus results in the following intensity distributions.

The relative intensity values at 0° and 20° in the 3rd beam are determined by how much of the reflector is allocated to each of the 2 parabolas. More specifically, each parabola gets some fraction of the total reflector angular extent. The total angular extent is the angular sweep about the focus from the bottom to the top of the reflector. In this case, it’s about 53°.

The reflector above with sections aimed at both 0° and 20° allocated 40% of the total extent to 0° and 60% toward 20°. Changing that allocation to 20% / 80% results in the following intensity distribution.

Since less of the reflector is collecting and redirecting light from the LED toward 0°, the intensity in that direction is reduced relative to the intensity at 20°. So in addition to the parametric reflectors allowing you to define the range of angles over which the reflector is aimed, they also allow you to manipulate the fraction of the reflector aimed toward each angle in the distribution. This is done by assigning a set of “weighting factors” to each reflector “aiming section.”

The reflector below shows a more realistic design, with aiming sections ranging from 0° to 20°, every 1° in between. This reflector is therefore comprised of 21 parabolic profiles all joined together. The weighting factors (WF’s) were defined so that they created a beam with a peak in the beam center that tapered off toward the wider angles in the distribution.

The image below illustrates the geometric input parameters for a reflector, including +/- angular conventions. The Lamp Center is the focus of the optic, the Nadir Direction defines the beam center, and the Start Point defines the fixed end of the reflector. The start point can be set at the top or bottom of the reflector. The Angular Extent defines the total angular size of the reflector. The “end point” of the reflector floats along the angular extent cutoff line with a location based on the profile shape, which is driven by the aiming parameters.

The aiming method is selected as “by angle” or “by point.” When using “by angle,” the angular conventions are as defined in the above image. When using “by point,” you enter the absolute points in the sketch or construction plane. Aiming angles are defined for each end of the reflector, with an Aiming Angle Increment that determines the total # of reflector sections between the 2 extremes. Aiming points are defined for each end of the reflector, with the Number of Points used to define the total # of reflector sections

Creating a Reflector

Reflector PODT Window / Dialog

All the parameters of an optical profile can be viewed and modified in the Solidworks PODT window or the Rhino PODT panel.

SOLIDWORKS

Rhino

Aim by angle - The aiming angles for the start & end of the reflector as well as the angular increment between the 2 extremes. The angles are measured from the nadir direction. Click "Update Aiming" to apply changes.

Aim by point - The start & end aiming point locations within the sketch/construction plane coordinate system, as well as the number of points in between. Click "Update Aiming" to apply changes.

Optical center X/Y - The focus of all reflector aiming sections in the sketch/construction plane coordinate system.

Start X/Y - The start point of the reflector in the sketch/construction plane coordinate system.

Curve resolution - The angular resolution of the polyline profile used to approximate the parabolic or elliptical reflector sections. The curve resolution defines the angular sweep about the optical center, starting from the beginning of each aiming section, at which vertices of the polyline profile are obtained. To get a reflector profile that closely approximates the parabolic/elliptical profiles, use a small value such as 0.5° or 1°. To create a “faceted” reflector profile, use a larger value. To create a single facet for each aiming section, use an angle that is larger than the size of all aiming sections, such as 90°.

Angular extent - The full angular extent of the reflector, measured about the optical center and beginning at the start point. CCW is a positive angular sweep, CW is negative.

Number of sections - The number of aiming sections determined by the aim by angle or aim by point parameters. This value can be overridden if you need to add or subtract sections from what the aiming parameters defined.

Calculate weights - A value of “On” enables the use of the weighting factor (WF) equation.

Weight exponent - Exponent in the WF equation. A higher positive value directs more light toward wider angles. A lower negative value directs more light toward the beam center. A value of 0 sets all WF’s to the minimum value.

Weight minimum - Sets a minimum WF value in the nadir (0°) direction.

Weight shift - Shifts the angle in the cosine function of the WF equation. Useful when your beam is directed toward a surface that is not centered about the nadir direction. For example, when illuminating a vertical wall with a ceiling mounted luminaire, using a weight shift of 90° produces a more useful trend in the WF’s.

Weight adjustment - An adjustment factor that can be applied to the calculated weights for each aiming section.

Lens Design Tool Overview

The lens design tool shares the same aiming and weighting factor parameters as reflectors, but uses refraction instead of reflection to redirect the light. Because lenses/refractors control light differently, they require different geometric constraints.

Whereas reflector shapes are determined by their aiming parameters, lens shapes are more flexible and generally defined by the style of the optic. For example, the prisms shown in the image above could be “mapped” to the flat “base profile” shown or a curved “base profile” like shown below depending on the style of the optic. The same type of aiming can be defined for either “base profile,” but the prism geometry will vary depending on shape of the base profile. To accommodate different styles of optics for any given application, the “base profile” is one of the input parameters.

Lens designs also require a material index of refraction and the material thickness since the light will refract through 2 surfaces. All lenses start as prismatic profiles as shown in these images. Once the initial lens definition is created, a larger range of parameters are available to modify in the PODT window, as described in the following sections.

Creating a Lens

Lens PODT Window / Dialog

All the parameters of an optical profile can be viewed and modified in the Solidworks PODT window or the Rhino PODT panel.

SOLIDWORKS

Rhino

Aim by angle - The aiming angles for the start & end of the base profile as well as the angular increment between the 2 extremes. The start and end points refer to the way the profile was drawn. The angles are measured from the nadir direction. Click "Update Aiming" to apply changes.

Aim by point - The start & end aiming point locations within the sketch/construction plane coordinate system, as well as the number of points in between. The start and end points refer to the way the profile was drawn. Click "Update Aiming" to apply changes.

Optical center X/Y - The focus of all refractor aiming sections in the sketch/construction plane coordinate system.

Profile type - Stepped creates a prismatic lens, Smooth creates a smooth lens. The smooth lens profile is anchored at the “start” of the profile. The smooth lens profile is created by connecting the sloped prism faces together, thus removing the riser steps. Since this adds thickness to the lens, be sure to draw the base profile with the appropriate start point based on which end of the lens profile needs to remain anchored in place.

Index of refraction - The index of refraction used to determine all prism/curvature computations based on the aiming parameters.

Number of aiming sections - The number of aiming sections determined by the aim by angle or aim by point parameters. This value can be overridden if you need to add or subtract sections from what the aiming parameters defined.

% control inside - The final refracted light direction results from light refracting into the inner lens surface and out of the outer lens surface. The initial inner and outer profiles are offset versions of the base profile. Prismatic elements are added to the base profile shape on the inner, outer or both surfaces as defined by this parameter. The images below show the effect of this parameter on a smooth lens profile that connects the prismatic elements together. Note that the start of the base profile was on the right side, which is why that point is fixed in all lens variations.

Number of prisms - The minimum number of prisms or steps along a smooth profile. This value is overridden by the # of aiming sections defined since each aiming section requires at least 1 prism or segment along a smooth profile. Use a value higher than the default to create more prismatic features or a smoother smooth lens profile. As seen in some of the prismatic lens images, the size of the prisms may change along the profile. This is a result of keeping all prisms below an internally determined max height. When a prism is determined to go beyond the max height, it is subdivided into 2 prisms. Setting a higher # of prisms can result in a smoother transition in prism sizes along the profile.

Use pull direction - Enables the adjustment of the prism risers based on the tool pull direction vector & draft angle. This parameter is only used for “stepped” (prismatic) profiles. The angle of the risers is oriented along radial lines back to the lamp center by default. This can result in prisms with undercuts on the inner lens surface as shown in the first image below. This is OK for extruded lenses, but not an injection molded lens. The image on the right shows how the prism riser angles change when a vertical pull direction is used.

Pull direction X/Y - Defines a direction vector for the pull direction in the sketch/construction plane coordinate system. The image above uses a pull direction X = 0 and Y = 1.

Draft angle - The angle away from the pull direction used to define the prism riser angle.

Peak/Valley fillet radii - The radius of curvature for the fillets used on the peaks & valleys of the prism steps. A value of 0 indicates no fillets will be used, thus all prisms will have sharp peaks & valleys.

Fillet resolution - Fillets are approximated by polyline segments. This parameter defines the angular resolution of the fillet curvature approximation.

Outer/Inner bulge angular extent - Prisms & segments of smooth refractor profiles are flat by default. A “bulge” is an arc shaped curvature added to the flat segment. Bulges create beam spread through each prism/segment. The curvature of a bulge is defined by the angular extent of the arc about the arc center. Thus, the steepest angle away from the flat prism/segment profile is at either end of the arc, with an angle of half the angular extent. See example below that has an angular extent of 40°. For materials with an index near 1.5, light refracts at about half of the profile tilt angle. Therefore, if you want to add 10° of beam spread to either side of the refracted ray directions through your prisms/segments, then enter an angular extent of 40°, 4 times the desired beam spread. The bulge parameters can be defined for the entire optic or individual aiming sections.

Bulge resolution - Bulge arcs are approximated by polyline segments. This parameter defines the angular resolution of the fillet curvature approximation.

Offset style - The method by which the offset profile is placed. “Simple offset” creates a copy of the base profile perpendicular to the base profile. “Radial from lamp center” creates a scaled version of the base profile along lines from the optical center to the start and end points of the base profile.

Offset distance - Distance from the base profile start point to the offset profile start point. This is initially set to match the minimum thickness, but may be increased when using a smooth profile and other points along the profile get closer than the minimum thickness to the base profile. Note that this value will not automatically change to find smallest value that meets the minimum thickness requirement as design changes are made. To find the smallest allowable offset distance, enter a value of 0.

Offset direction - Specifies the offset profile direction, to the inside or outside of the base profile.

Minimum thickness - Minimum distance between the inner and outer lens profiles.

Calculate weights - A value of “On” enables the use of the weighting factor (WF) equation.

Weight exponent - Exponent in the WF equation. A higher positive value directs more light toward wider angles. A lower negative value directs more light toward the beam center. A value of 0 sets all WF's to the minimum value.

Weight minimum - Sets a minimum WF value in the nadir (0°) direction.

Weight shift - Shifts the angle in the cosine function of the WF equation. Useful when your beam is directed toward a surface that is not centered about the nadir direction. For example, when illuminating a vertical wall with a ceiling mounted luminaire, using a weight shift of 90° produces a more trend in the WF's.

Weight adjustment -Y An adjustment factor that can be applied to the calculated weights for each aiming section.

TIR Collimator Design Tool Overview

“TIR Collimator” lenses were developed to provide full control of LED light emitted into a single hemisphere. This general lens type is called a “TIR collimator” since the lens features a Total Internal Reflection (TIR) reflecting surface and many initial versions of this type of lens were intended to convert the broad Lambertian emission of an LED into a narrow “collimated” beam. The main features of a TIR collimator lens include an outer profile that reflects light via TIR and a central lens feature that controls light via direct refraction. The basic functionality of a TIR collimator lens is shown in these 2 images:

The raytrace shows the inherent advantage of a collimator lens over an open reflector since all rays are controlled, not just the rays captured by the reflector. The TIR surface also reflects with no losses. The TIR surface is important since this allows narrower beams to be created compared to what is possible through direct refraction alone.

Light doesn't need to be aimed toward a single direction with a TIR collimator lens. The TIR reflector surface and central lens feature can aim light toward any desired range of angles.

There are many styles of TIR collimator lenses and Photopia provides 4 to choose from. The one above is called “Outer Shaft” while the “Double Shaft,” “Inner Shaft” and “Stepped” versions are shown below.

Each collimator style has some advantages and disadvantages, so you choose the best style depending on your design performance priorities and design constraints. Also note that the inner shaft collimator is just a variation of the double shaft collimator. So these 2 styles share the same parameters as described below, but use different default values.

The following images show a range of parameters that can be defined for each of the collimator styles.

Creating a TIR Collimator

TIR Collimator Window / Dialog

The PODT panel includes some additional parameters, grouped into Optical, Mechanical & Aiming categories.

Exterior refractive index - The default value is 1.0, the value for air. If the collimator lens will be used within a different medium, then the outside index of refraction can be changed to another value. This affects all refracted rays entering and exiting the collimator lens, but does not affect the TIR surface, which always assumes a TIR reaction. Thus, setting this index to a higher value for water, for example, assumes water all around the lens except for the TIR surface, which still assumes an outer medium of air.

TIR curve resolution - Used in conjunction with the TIR profile aiming properties to define the angular resolution of the straight line segments used to construct the TIR profile when the “degree of the curve's spline” is set to 0 or 1 (expert mode required). A value larger than the angular size of each TIR profile aiming section will result in a single line segment for each aiming section.

Number of central lens segments - Used in conjunction with the central lens aiming properties to determine the number of straight line segments used to construct the central lens feature when the “degree of the curve's spline” is set to 0 or 1 (expert mode required).

Percent control inside - (Only for double and inner shaft collimators) When using a double shaft collimator, this allows you to control the percent of the refraction done on the inner and outer surfaces of the central lens feature. Shifting more control to the outer surface can help narrow the beam angle since the angular size of the lamp will be smaller for the lens surface controlling more of the light.

Outer shaft - (Only for double and inner shaft collimators) Included or Hidden. If included, then the percent control on the inside surface can be any value between 0 to 100%. If hidden, then the percent control on the inside surface is forced to 100%.

TIR Collimator Aiming

TIR collimator lenses include separate aiming properties for the TIR profile and central lens features. The aiming parameters are simplified from those available for general parametric reflectors and lenses, with light aimed by angles. The start, end and aiming angle increments are defined for both parts of the collimator. The weighting factor equation values are also defined for both parts of the collimator.

The aiming angles specified for the TIR profile define the “net” aiming desired for light exiting the lens. The TIR profile aiming is automatically adjusted to account for light refracting into and out of the collimator lens.

The image below shows the aiming angle conventions, start points for each feature and the color scheme used to graphically indicate the weighting factor plots for each feature.

This image shows how the aiming properties are defined for the TIR and central lens features and how their weighting factor plots are displayed in the CAD view, along with their aiming angles.

PODT 3D Surface Creation

Modifying a Design

Spherical Lens Tool

Create a Spherical Lens

Modifying a Spherical Lens

Placing a Spherical Lens

Limitations for Spherical Lenses

Weighting Factors

When the goal of the optical design is to achieve a specific intensity distribution, you need to define both the directions over which the light is aimed as well as the amount of light aimed toward each direction. The aiming parameters defined for reflectors and lenses cover the former. Weighting factors cover the latter.

The weighting factors (WF's) indicate the relative importance/size of each aiming section of the optical profile. The way the WF's work is illustrated in the reflector profile image below. Each reflector section is aimed toward a unique angle in the beam and is assigned a relative WF value. The absolute magnitude of the WF's isn't important, only their relative values with respect to each other. The fraction of the reflector Angular Extent that is allocated toward each aiming section is determined by dividing the WF for that section by the total of all WF's.

The value of this system is that it allows for quick relative changes to your design by changing a single value. For example, if you need more light at the widest aiming angle, then you simply increase that WF. That aiming section increases in size, while all the rest proportionally shrink. The example above shows higher WF values at the wider aiming angles. These result in a higher fraction of the angular extent allocated to the wider aiming angles.

The rules apply in the same way to lens optics. In their case, the angular extent is the full angle subtended by the Base Profile about the lamp center. The angular extent determined for each aiming section based on their WF's is then projected onto the base profile.

Weighting Factor Equation

Smoothly changing beams are often required for many applications. These are generally achieved with smoothly changing WF’s, which result in smoothly changing optical profile geometry.

Although WF’s can be entered manually, Photopia provides a WF equation that creates useful trends of smoothly changing WF’s over the entire distribution. For example, if you need to produce even illuminance/irradiance values over a surface below your optic, then you will need an increasing intensity at wider beam angles. This requires WF’s that increase at a user defined rate as a function of the angle away from the beam center. Conversely, if you require a narrower beam optic with the peak in the beam center, fading to a desired beam angle, then you need WF’s that peak at the beam center and decrease at a user defined rate at the wider beam angles. The WF equation has parameters that allow for these types of distributions and more. Understanding the WF equation is important since it allows you to make desired changes to your entire set of WF’s by changing a single parameter of the equation.

The core of the WF equation is:

Where ϴ is the angle in your intensity distribution. We chose this starting point for the equation since it has the trend of increasing WF’s at wider beam angles, a commonly desired beam trend. The following images show a quick review of the cosine function. It’s the x-component of the radius of a circle as it rotates counter-clockwise from the X-axis. It starts at 1.0 at ϴ=0°, the beam center, and drops to 0 at ϴ=90°.

So the inverse of the cosine function increases non-linearly as ϴ goes from 0° to 90°. Since the equation divides by 0 at ϴ=90°, the WF value is capped to a maximum of 100.

To add more flexibility to this equation, such as defining the rate at which the WF’s increase at wider angles, an exponent n was added to the cosine function:

As n increases, the WF increases at a faster rate at the wider beam angles, thus more light is directed toward the wider beam angles and less toward the beam center. This results in intensity distributions with trends such as this.

If a negative exponent is entered, then the equation inverts so that the highest WF is at ϴ=0°. Decreasing n to lower negative values causes a greater emphasis of the WF in the beam center. Negative n values create beams with trends like this.

Two more parameters were added to the WF equation that allow you to explicitly define the value at ϴ=0° and rotate the frame of reference when illuminating surfaces that aren’t horizontal below your optic. The WF 1.0 equation adds some absolute values to avoid negative WF values. The WF 2.0 equation doesn’t apply any absolute values and simply sets the WF to 0 if the equation produces a negative value. This works well to automatically remove wider aiming angles as the exponent goes to lower negative values, which is common when designing a narrower beam angle. The WF 1.0 equation was the default through V2023 while WF 2.0 is the default from V2024 forward. The final equations are shown here:

Where:
WF = weighting factor
ϴ = angle in the distribution
n = Weight exponent
Min = Weight minimum (defines the WF at ϴ=0°)
α = Weight shift (angular shift in cosine function)

While it’s best to define your entire set of WF’s with the equation whenever possible, there are times when you need to manually adjust WF’s in specific parts of the beam. Multipliers are therefore provided for each aiming section of your optic.