As interest in using light disinfection continues to grow standard setting organizations and manufacturers are becoming more active in this area. The International Commission on Illumination (CIE) has just released a position statement on the use of ultraviolet radiation to manage the risk of COVID-19 transmission.
Here are a few bullet points:
While ultraviolet light ranges from 400 nm to 100 nm, the most effective wavelengths are at around 254 nm and this is generally what is meant by germicidal ultraviolet or GUV.
UV-C has been successfully used for water disinfection and in air handling units for many years. UV-C has also seen a resurgence for use in healthcare environments.
Direct exposure to UV-C can cause photokeratitis (similar to snow blindness) and erythema (skin reddening similar to sunburn) so carefully shielded luminaires are required when used in occupied spaces.
Consumers should be wary of products not approved by consumer safety organizations. Such products could be hazardous to use or may not emit UV-C at all.
Today’s post was going to be a reminder to take manufacturer provided education with a grain of salt. Last week I sat through a manufacturer’s presentation on color. There were some big errors and some that’s-not-quite-right errors that angered me. The information presented wasn’t hard to confirm, but whoever created the presentation didn’t so some of it was wrong. However, before I could start writing I received an email about a new color quality metric that was developed by Bridgelux. Here’s the scoop.
Last Thursday, May 14th, Bridgelux announced a new metric, Average Spectral Difference (ASD), which they claim quantifies the naturalness of a light source. The announcement is based on this white paper by Bridgelux. The white paper asserts that since we evolved under fire light and day light, human-centric lighting should use spectra that mimic these “natural” sources. Bridgelux says that, “ASD provides an objective measurement of how closely a light source matches natural light over the visible spectrum, averaging the differences of the spectral peaks and valleys between a light source and a standardized natural light source of the same CCT.”
Basically, ASD is a measurement of the difference between a “natural” spectrum and that of an electric light source. It is expressed as a percentage, with lower percentages equaling a closer match to the reference source and higher percentages equaling a larger difference between the two.
My first thought was, “Oh, it’s CRI – Natural Edition” but in some ways it’s even worse. For starters, while Bridgelux presents a definition of “natural” light that is based on the illuminants we use as references for color fidelity calculations, there is no accepted definition of “naturalness” in the lighting industry, or most other industries for that matter. Obviously, a metric for something that has no industry-wide definition is of questionable value. The white paper says, “The reference source used by Bridgelux is the blackbody curve (BBC) for light sources of 4000K and below, and the daylight spectrum (i.e. standard illuminants such as D50, D57, and D65) for light sources of 5000K and above.” (Yes, there’s an obvious typo there because they’ve left a gap between 4000 K and 5000 K.) Second, like CRI it presents a single number with no additional information about where in the spectrum the differences occur, or if they are increases or decreases relative to the reference light source. Third, as a measurement of spectral difference alone, it disregards the fundamentals of human vision, including the principle of univariance and how perception changes with intensity, among other things.
I emailed a few colleagues on the IES Color Committee and found that they were already examining ASD. Some of the comments that came back were, “This is just a refresh of a spectral bands method. It says little about color rendering” and “This is very similar to the Film industry’s SSI developed by the Academy. It also suffers from the same problem. If the result isn’t 0% (or 100%) then it tells you nothing about where the differences are. Thus, it tells you nothing about whether two light sources will work together.”
Michael Royer at PNNL went further by looking at ASD with the sets of data in TM-30 Annex F that were used to develop the TM-30 Annex E recommendations. Here’s what he had to say. (You may have to right click and open the graphs in a new tab to see them clearly.)
First, spectral similarity metrics are not new at all—they predated CRI (e.g., Bouma spectral bands method from 1940s). For some reason they gained popularity again in the last decade or so. Here are some other examples:
B. H. Crawford. 1959. Measurement of Color Rendering Tolerances J. Opt. Soc. Am. 49, 1147-1156
Crawford, B. H. 1963. Colour-Rendering Tolerances and the Colour-Rendering Properties of Light Sources. Transactions of the Illuminating Engineering Society, 28: 50–65.
Kirkpatrick, D. 2004. Is solid state the future of lighting?” Proc. SPIE 5187, Third International Conference on Solid State Lighting.
Acosta I, Leon J, Bustamante P. 2018. Daylight spectrum index: a new metric to assess the affinity of light sources with daylighting. Energies 11 2545
Spectral similarity measures, like ASD, don’t relate to perceived naturalness or preference at all. They’re more closely correlated with color fidelity (e.g., Rf) but perform even worse in terms of correlation with perceived qualities because they don’t account for how the visual system works (they might have more use for understanding cameras, as used by SMTPE with SSI, linked above). I guess people just assume that a Plankian/Daylight spectrum is ideal. While smooth SPDs have advantages, Planckian/Daylight SPDs aren’t perceived as more natural or more preferred in typical architectural lighting scenarios. This has been shown over and over in experiments, where it’s become quite evident that certain deviations from Planckian are preferred/viewed more natural than others.
Here’s the correlation between ASD and rated naturalness/normalness, preference, and Rf for the three datasets used to develop TM-30 Annex E:
If you’re not up on your statistics, r2 is a measurement of how well data fits to a prediction or to the data average. 1.0 is a perfect fit. Generally, 0.7 or above indicate a strong statistical correlation, and values less than 0.3 indicate no relationship.
PNNL (combination of three studies):
Zhejiang:
Penn State:
Overall, it’s clear that ASD isn’t a tool for characterizing perceived naturalness (or preference) over a wide range of SPDs, and it probably has limited other uses. While spectral smoothness (as exemplified by the reference illuminants in ASD) is sometimes a useful goal, there are other metrics more rooted in human vision to better asses this characteristic. It’s a shame that ASD and the accompanying message will likely lead to confusion, especially when there’s enough to learn about color rendition already.
This is a good example of why it’s important to rely on metrics that have been vetted through a standardization process and to always be skeptical of marketing material.
So there you are. Take manufacturer’s education with a grain of salt. The same is true of their internally developed metrics. I’m not saying that they are intentionally deceiving anyone. but their goal is sales, not education. As Mike points out, this is why metrics need to go through a vetting process before we can use on them with confidence.
By the way, although I’ve mentioned the IES Color Committee and quoted a few of its members, this post doesn’t represent the opinions of the committee or of the IES.
This Saturday, May 16th, is the International Day of Light, a UN backed global initiative that provides an annual focal point for the continued appreciation of light and the role it plays in science, culture and art, education, and sustainable development, and in fields as diverse as medicine, communications, and energy. May 16th was selected because it is the anniversary of the first successful operation of the laser in 1960 by physicist and engineer, Theodore Maiman.
Unfortunately, Day of Light activities around the world are few. One that begins today is the IES Virtual Research Symposium. Held bi-annually, this year the title is LIGHT+ QUALITY – Meaningful Metrics Beyond Energy. If you’re interested, you can register here.
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.
LEDucation this year is on March 17 and 18 at the New York Hilton Midtown where I’ll be part of two presentations. The first, at 9 am on Tuesday morning with Wendy Luedtke of ETC, is a seminar called Specifying Color Rendering with TM-30’s New Annex E. The session presents the new ANSI/IES TM-30 Annexes E and F, which apply recent research to identify three color rendering design intents (Fidelity, Preference, and Vividness) and provides specifiers with TM-30 values to achieve them alone or in combination. Our goal is to increase awareness of Annexes E and F and to help attendees better understand their contents and use. The seminar is most appropriate for people with some prior knowledge of TM-30, although there will be a brief TM-30 overview for those who are new to the topic.
Then, on Wednesday, we’ll be joined by Jess Baker of Schuler Shook for a daylong demonstration of Annex E. In the TM-30 Demo Room visitors will experience an immersive mockup illuminated with a variety of light sources illustrating the Annex E design intents. The lighting demonstrations will be paired with TM-30 values to show how TM-30 can be used to select light sources for each intent. Visitors will experience sources that meet different levels of the IES TM-30 specification guidelines outlined in IES TM-30-18 Annex E. We’ll be presenting the demonstration on the hour and half hour from 9 am to 2 pm.
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 eight color samples.
Colors used to calculate CRI Ra
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.
TM-30 99 color evaluation samples (CES)TM-30 CES spectral reflectance functions
It also breaks the color space up onto 16 Hue Bins, each one covering a specific range of the color space. 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.
TM-30 hue binsExample of TM-30 chroma shift bar graph by hue bin
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.
In 2007 Congress passed the Energy Independence and Security Act (EISA) with the goal of increasing energy efficiency across the economy. Part of EISA has affected the lighting industry in the form of mandated efficacy of light sources. The initial efficacy rules targeted A-Lamps (standard household light bulbs) and set the efficacy level above that of incandescent but below that of halogen lamps. The result was a slow shift to the more energy efficient technology. Over the years the energy efficiency requirements have been expanded to more lamp shapes, always in keeping with technological ability so that we never faced a lamp shortage or loss of a lamp shape. Today, more than 50% of lamps sold are LED that exceed even the most stringent requirements.
On September 4th the administration announced that it was going to cancel a new set of requirements that would have taken effect in January 2020 that would have applied to products such as decorative medium base lamps and MR type lamps. In my opinion, this is another example of the administration cutting off its nose to spite its face. As with the threat to “investigate” automakers who agree with the State of California’s proposed energy efficiency requirements, this effort to undo energy efficiency despite the monumental consensus that we need to reign in our energy consumption isn’t going to go have any effect. No lamp manufacturer is going to reopen or build new factories to make incandescent lamps when it’s obvious that A) the next administration is going to reinstate the efficacy requirements B) the public has embraced the energy savings of LED lamps, and C) the companies know that it would be bad for their image to turn their backs on mitigating climate change.
