Due to growing concerns of COVID-19 in the lighting industry and the New York community, the Designers Lighting Forum of New York is postponing the LEDucation 2020 Trade Show and Conference that had been scheduled for March 17 – 18.
LEDucation is being rescheduled to August 18 – 19, 2020. I expect that our TM-30 Annex E seminar and demonstration room will be part of the rescheduled event.
Recently, ANSI/IES TM-30 was improved with the addition of Annexes E and F. Annex F reviews and summarized five studies that explored using TM-30 metrics to predict subjective visual outcomes. Annex E uses that research to establish recommended specification criteria when the designer’s color rendering goals are Preference, Vividness and/or Fidelity.
I’ve been using Annex E on projects and have spoken to other designers who have begun to use it. It provides useful, accurate information that allows me to evaluate the color rendering results of light sources in a way that hasn’t been possible until now. It lets me make informed decisions about my projects, and explain those decisions to colleagues and stakeholders in (relatively) easy to understand terms.
TM-30 and the TM-30 calculators continue to be a free download from the IES here. Annexes E and F are also free on the Errata and Addenda page here and here.
Last Thursday Donald Trump spoke to a group of Republicans in Baltimore. One of the things he said caught my attention: “The lightbulb. People said what’s with the lightbulb? I said, here’s the story. And I looked at it, the bulb that we’re being forced to use, No. 1, to me, most importantly, the light’s no good. I always look orange. And so do you. The light is the worst.”
Now, I’m not aware of being made to look orange under LEDs, nor have I ever noticed LEDs making my friends, colleagues, or students appear orange. You can’t imagine how embarrassed I’d be if it turned out that a real estate developer and entertainer had more astute color perception than me, a lighting designer and Co-Chair of the IES Color Committee. If our only means of evaluating the color rendering of a light source, and evaluating the orange content specifically, was CRI we would have no objective way of testing his statement. CRI, technically Ra, is a single value that gives us an average of the match between the light source in question and its reference source (either a blackbody radiator or a CIE definition of daylight, depending on CCT) using only the eight color samples shown below.
Since Ra is an average value there’s no way to understand the rendering of any particular hue. I’ve talked about this here. However, one of the wonderful things about ANSI/IES TM-30 IES Method for EvaluatingLight Source Color Rendition is that we can use it to test that claim. TM-30 uses 99 color samples that are distributed across the color space and the visible spectrum, as shown below.
It also breaks the color space up onto 16 Hue Bins, each one covering a specific range of the color space, again as shown below. In the case of orange, we want to look at Hue Bin 3. Specially, we want to look at Rcs,h3 (the subscript CS stands for Chroma Shift) which quantifies the increase or decrease in the saturation or vividness of orange compared to the reference light source.
So, let’s put the science of TM-30 to work and see if we really do know that LEDs make us look orange!
The TM-30 calculator contains a library of 300 SPDs (spectral power distributions), of which 137 are commercially available white LEDs. The CCTs range from 2776 K to 6123 K. If white light LEDs really did make us look orange we’d expect to see a large majority of them have a positive Rcs,h3, probably with an average chroma shift in excess of 10%. In fact, the 137 SPDs have Rcs,h3 that range from -8% to 1% with an average of -3.6%, a decrease (not an increase) in the saturation of orange. It’s not me, it’s him. TM-30, which uses the most modern models of human vision and a set of colors that cover the color space and visible light spectrum, proves it. What a relief!
Don’t believe me? Download TM-30 and the calculator for free from the IES web site and see for yourself.
Of course, I’m not saying LEDs are perfect light sources. Like any other product there are good ones and bad ones. However, TM-30’s measurements of fidelity and gamut (as averages) and measurements of fidelity, chroma shift, and hue shift (by hue bin) permit us to make a thorough evaluation of a light source to understand its color rendering characteristics. Using this knowledge, we can determine if a particular light source distorts colors and is appropriate for a project, or not.
I should take a moment to note another error he made when he said, “And very importantly—I don’t know if you know this—they have warnings. If it breaks, it’s considered a hazardous waste site. It’s gases inside.” Perhaps you’ve heard the acronym SSL or the phrase solid state lighting. LEDs are a version of SSL, which means that they are…well, solid. Unlike previous light producing technologies LEDs are a solid combination of materials. As such, if one were to physically break (which is unlikely since LEDs are small, are mounted to a heat sink and often covered with a lens, so you’d have to break a lot of materials simultaneously) no gas, hazardous or benign, is emitted. He’s thinking of fluorescent lamps and the small amount of mercury they contain. Even then, a broken fluorescent lamp doesn’t turn the area into a” hazardous waste site.” Here are the EPA’s instructions for cleaning up a broken fluorescent lamp.
This year’s IES Annual Conference in Louisville, KY runs from August 8 to 10 and will include two events to help specifiers better understand ANSI/IES TM-30 IES Method for Evaluating Light Source Color Rendition.
On Friday, August 9th there will be a seminar on the soon to be released TM-30 Annexes E and F, presented by Michael Royer of PNNL, Tony Esposito, and me. Annex E is a set of guidelines for TM-30 values for several design intents. Annes F is an analysis of the research that underpins the Annex E guidelines.
On Friday and Saturday we will also have a demonstration room where specifiers can experience a range of TM-30 values in office and retail settings.
Last Friday I took my class on a visit to a fixture manufacturer’s showroom. The visit was pretty successful, but I had one issue with the information that was presented. This manufacturer’s rep presented their CRI 80 and CRI 90 products by saying that CRI 80 dulls colors and CRI 90 makes colors “pop”. I can’t blame him too much, after all it’s a common misconception that higher CRI is “better.” However, it’s not true so let’s take a look.
CRI (or more formally, CIE 13, Method of Measuring and Specifying Colour Rendering Properties of Light Sources Ra) is a fidelity metric. That means it calculates the color rendering of a light source in comparison to the color rendering of a reference light source of the same color temperature or correlated color temperature (CCT). A light source with a CRI 80 renders colors with more color error (that is, a larger mismatch or a larger color appearance error) than does a light source with a CRI 90. That’s all. One of the problems with CRI, which is addressed in TM-30, is that a single number value doesn’t tell us the hue(s) where there is a color rendering error compared to the reference light source, nor do we learn the direction or the degree of color rendering error(s). In other words:
What hues are not rendered accurately? CRI doesn’t tell us.
Are those hues made to appear more or less saturated? CRI doesn’t tell us.
Are those hues shifted toward an adjacent hue? CRI doesn’t tell us.
TM-30 (ANSI/IES TM-30-18 IES Method for Evaluating Light Source Color Rendition) does give us this information, which immediately puts to rest the notion that higher fidelity is “better” color rendering in all cases.
It’s entirely possible for a light source with a CRI 80 to render a set of colors more vividly than a CRI 90 light source if the color errors increase saturation and minimize hue shifts. It’s even possible for two light sources of the same CRI to render colors differently. Here’s an example. The first light source has a TM-30 Rf (fidelity) of 90 and an Rg (chroma) of 99, meaning that on average colors are rendered slightly less vividly than the reference light source. The TM-30 Color Vector Graphic shows us clearly that the rendering of red (Bin 1) is less saturated than the reference, and that the rendering of warm blue (Bin 12) is more saturated. The other colors are a nearly perfect match to the reference source.
The second source also has an Rf 91. However, the green and purple hues are rendered with increased saturation so that it has an Rg 105. (Yes, the CCTs are different, but that doesn’t matter because in the calculation a light source is compared to a reference light source of the same CCT, cancelling out any color errors due to CCT.)
Understanding this information opens the door to considerations other than fidelity. The first is vividness. Are you lighting the M&M store in Times Square? If so, your design goal may be to increase saturation of the candy, not accurately render it. In that case you’re going to want a lower fidelity (Rf) so that you can get higher chroma (Rg). The light source shown below might be just the one for this application.
The second is preference. Studies have shown that in many applications people prefer slight increases in chroma, especially in the red range. Are you lighting a restaurant? If so, and if preference and increased red chroma are important, this might be the light source for your project:
The increased information TM-30 provides is both more accurate and more detailed than CRI. Not only that, it gives us a deeper understanding of the color rendering capability of a light source and allows us to consider design goals other than fidelity. Designers who care about these color considerations need to keep pushing manufacturers to provide TM-30 information and train their employees in its meaning and use.