Jun 23, 2022
By Michael Royer and Jess Baker
The IES recently released an online spectral calculator as part of its digital Standards Toolbox, which is available at www.ies.org/tools. Lighting specifier Jess Baker asks Michael Royer about how it came to be, how it works, and how it could change one small but important aspect of lighting practice.

What does this tool do?

The tool currently calculates IES TM-30 color rendition metrics and CIE S026 metrics, including the CIE-standardized version of the “M/P ratio,” melanopic Daylight Efficacy Ratio (mel-DER). It provides flexible data entry and produces standardized reports. A library can be used to store data for thousands of SPDs, and reports can be generated for any or all of them at once. For TM-30, the new tool provides all of the functionality of the older Excel-based calculators.
TM-30 Spectral Calculator
Example of a ANSI/IES TM-30 Color Rendition Simple Report generated from the TM-30 Spectral Calculator.

Why an online calculator?

Compared to the older Excel calculators, the web-based tool ensures that lighting professionals are always using the most up-to-date version of TM-30, allows for an expanded range of features, and is easy to find in a central location on the IES webpage. Because the online calculator is more centralized than the previous Excel calculator, it will be the standard reference calculator going forward. The IES Color Committee will no longer develop the Excel calculators.

Who is the calculator meant to be used by?

Everyone! Ideally, lighting manufacturers will use the calculator to generate data for all their products, which can be provided to specifiers or submitted to lighting specification programs like the DLC Qualified Products List. They can even share data for their full product lineup. But if a manufacturer doesn’t provide TM-30 or alpha-opic data, specifiers can easily use the calculator to get the information they need.

What kind of data do I need to input?

The tool takes a spectral power distribution (SPD) as input. It could be something you measure with a meter or something that’s provided by a manufacturer or third party. You can paste an SPD (wavelength and value) directly into a table, upload one or multiple .spdx files (see IES TM-27M), or upload lots of SPDs at once using a provided Excel template. The tool also allows users to create .spdx files, which are an easy way to transfer spectral data, functioning just like a .ies file for luminous intensity distribution data.

There’s lots of different reports and data output in the calculator. What’s the most important thing to look at?

The tool creates all of the standardized reports (i.e., TM-30 cutsheets) documented in TM-30 Annex D, from a quarter page to a full-page layout. It also has reports for alpha-opic data, and all the numerical data for both types of calculations can be downloaded. What’s most important to you may vary based on what you’re trying to do. The application does include tooltips that provide information about specific metrics, but it’s not meant to be a comprehensive guide; users should review the standards as needed—TM-30 is free. A recent FIRES blog addresses how to effectively pare down the wealth of TM-30 data, and the IES Color Committee is working on a new Lighting Practice (LP) document that will provide additional guidance.

Does the calculator store any of the data that is uploaded?

Any data you upload or calculate only exists while your Internet browser session is open. Once you close the tab or window, all the data is erased. This was a key request of some lighting manufacturers. To enable work over multiple sessions, individual SPDs can be downloaded as .spdx files. Entire libraries of calculated data can be saved locally as a .json data file (just a formatted text file). Either the .spdx file or the .json file can be re-uploaded by the same user or shared with others.

What are the best new features of this tool?

With the old Excel tools, SPDs had to be processed one at a time. With the online tool, a full library of SPDs can be uploaded and calculated, then the results can be sorted and filtered. Reports in one or more formats for some or all of the SPDs in the library can be generated with just a few clicks. Batch calculations are so simple! A big benefit is the ability to save .spdx and .json files to share with others. For example, a manufacturer could pair an .spdx file with each .ies file or could share a spectral library of their full product lineup by downloading one .json file.

Are there any additional features being developed?

Yes. While the initial release is out, the intent is to continue to add new metrics and new features over time. We’ve already received valuable input, and welcome more. Some users have requested the ability to compare performance for different SPDs (like online shopping), improved search of the library, a quick check against various specifications, and the ability to optimize SPDs. For metrics, there are plans to add calculations for CCT quadrangles based on ANSI C78.377, different chromaticity systems (i.e., xy, uv, u’v’), horticultural lighting metrics and more. We hope to build out the platform as a go-to source for any calculation that begins with a spectral power distribution.

How do you think this calculator will affect the lighting specification process in the future?

Broadly speaking, the professional lighting community has been slow to adopt new metrics. From 1931 chromaticity coordinates to CRI, the tendency is to stick with familiar methods, even once they’re outdated. One of the goals with this tool was to make it as easy as possible to generate and share data for new, improved metrics. This in turn can help manufacturers use new metrics to develop products and assist designers with their specifications. Together, these benefits can help save energy (both the electrical kind and the human kind) and improve the quality of the lit environment. In the next few years, I hope to see data for spectrum-based metrics much more readily available. This should allow for more carefully tailored color rendition specifications, for example, rather than specifiers being forced to choose from a limited basket of options.


Michael Royer

Michael Royer

Michael Royer is a Senior Lighting Engineer at PNNL, where he focuses on the development of LED technology. His emphases are human factors experiments and developing new metrics and test methods, especially for color, glare, flicker, and long-term performance. Michael is a... More info »
Jess Baker

Jess Baker

Jess Baker, Assoc. IALD, LC, Member IES, is a senior lighting designer and Studio Leader of Schuler Shook’s San Francisco Bay office. She is a member of the IES Color Committee and specializes in designing human-centric lighting and optimized color rendition... More info »