Distribution of Photopia Generated Photometric Files (IES, TM14, LDT)

As Photopia has come to be more widely used in the architectural lighting industry, an increasing number of Photopia generated photometric files are being distributed by lighting manufacturers to their customers. By photometric files, we are referring to IES files in North America and TM-14 or EULUMDAT in other regions of the world.

The original intent of Photopia was to allow manufacturers to develop new designs more quickly and more cost effectively by evaluating their design ideas on their computer instead of building and testing each and every design alternative. Once the predicted design performance met the desired criteria, a prototype was built and physically tested. If the physical test did not meet the design requirements, then modifications would be made until the requirements were met. In many cases, this involved troubleshooting the design to ensure it was built to specifications, so that it matched what was modeled in Photopia.

Photopia is no longer only used in the development of new standard products. It is also used to model the performance of custom luminaires where the time from concept to installation does not allow for the classic product development cycle. Additionally, it is being used to model some existing products for which photometric testing was never before required. In these cases and others, some manufactures will distribute photometric files generated by Photopia.

Whenever a photometric file generated by Photopia is distributed to a customer, the data should be as accurate as possible. The consequences of the photometric data not being accurate can be very costly if you are called out to fix an installed job. The distribution of inaccurate data also hurts Photopia's reputation and therefore its overall value. So it is in everyone's interest to ensure photometric data generated by Photopia is as accurate as possible.

While Photopia's accuracy has been confirmed by our own experience as well as that of our customers, the accuracy is dependent upon several critical factors, including but not limited to the following:

You need to build exactly what you have modeled. If you compromise and choose a similar lamp or materials to the ones you will actually use, then you can expect differences between the predicted and measured photometry.

You need to understand your manufacturing tolerances for all of the parts in your design. You can create a range of Photopia models for the expected range of part configurations to gain a better understanding of the expected range of photometric performance.

You need to understand how to use Photopia well enough to properly setup your analysis so you get accurate results. This means properly orienting your luminaire, using the proper angle set in the candela distribution, using the proper number of reflections and the proper number of rays. See this link for more information about photometric standards.

Some issues such as thermal effects are completely ignored by Photopia, so if you have thermally sensitive lamps then you know that there will be differences between the simulated and measured efficiencies.

Anisotropic materials are only supported in Version 3.0. So if you use a material with a significant grained texture such as Alanod Miro 5, then the anisotropic properties need to be accurately modeled within Version 3.0.

For more information about the factors that affect the accuracy, see Appendix C of the 2.0 User's Guide.

Guidelines for Distributing Photometric Files:

If you do distribute IES files generated by Photopia, then please follow this advice:

Leave the [TEST] keyword in the IES file exactly how Photopia has defined it. This will ensure that your customers know that the file is the result of a simulation and not a physical test.

Remove all lines with the [OTHER] keyword. This information is useful to the optical designer, but not necessarily to your customers. This data could invite questions from your customers about details of the analysis that are not important. You can edit the IES file in Notepad.

You should review the total luminaire watts as defined in the IES file. This value is set according to the default lamp and assumed ballast wattage for the Photopia lamp model. If you have more accurate information about the total luminaire watts, then use it. See the end of Appendix B of the User's Guide for the IES file format.

Be sure to let your customers know that the data is simulated when you distribute the files either in your e-mail or on your website so that there is no misunderstanding about this issue later on.

Thank you for your attention to this issue.

The Photopia Product Support Team