Last week Tony Esposito and I presented seminars at ArchLIGHT Summit in Dallas, TX. The topic was TM-30 and the deep information that it provides us about a light source’s spectrum and the resulting color rendering. CRI, of course, only evaluates fidelity – how close a light source matches its reference light source. But CRI penalizes all deviations and says nothing about the rendering of individual colors. Nor does it help us understand if the deviations from the reference are acceptable to viewers.
A small part of our demo is shown below. It illustrates how two light sources can have the same fidelity (in this case Rf of 70) but wildly different spectra that produce wildly different color rendering results. This is the great strength of TM-30, a deeper insight into the effect of a light source on illuminated objects and their color appearance – not just fidelity, but chroma shift, hue shift, and the perceptual implications of those shifts.
The video below shows the color appearance shifts. The graphic illustrates that even though the Rf is 70, the first light source renders objects in a preferred manner (Preference Priority Level of 3 or P3) and increases vividness (Vividness Priority Level of 2 or V2). At the same Rf the second source mutes colors and fails to achieve any of the Design Intents and Priority Levels specified in TM-30’s Annex E.
The pandemic has certainly distracted me from regular posting here. I’m probably not back to posting weekly, or even monthly, but I do have a new topic and a few things to say about it. The topic is color science as it applies to lighting.
No doubt you’ve seen something like Figure 1 before. It’s the CIE 1931 (x, y) chromaticity diagram and is the most common graphic for showing the range of tunable white luminaires and LED colors and their color mixing possibilities.
The thing is, we keep using this diagram even though it has problems and has been replaced twice. The problem is that it isn’t perceptually uniform, which means that the distance between any two color points doesn’t correspond to the perceptual difference between those two colors. This was famously demonstrated in 1942 by David MacAdam as shown in Figure 2. Using 25 chromaticities he had a trained observer, using a device that allowed for the color adjustment of light, attempt to create a side-by side match from different starting points – for example match a yellow sample starting from green, then match it again starting from red, etc. When he plotted the results in CIE 1931 (x, y) the area where color differences could not be detected formed an ellipse as shown in Figure 3. This demonstrated that the color space was not perceptually uniform. If it was the ellipses would have been circles.
These “MacAdam ellipses” have become the default way manufacturers talk about color consistency of their products. You’ll often see statements on cut sheets saying that the LEDs for a particular product line all fall within an X-step MacAdam ellipse (2-step, 3-step, etc.). Want to hear something crazy? In 2014, the International Commission on Illumination (CIE), which sets the standards for most things related to color and light, recommended ending the use of MacAdam ellipses. Why? Look at Figure 2 again. The size of MacAdam ellipses changes as we move around the chromaticity diagram. So does anything related to them, such as Standard Deviation Color Matching (SDCM) another, although less common, measure.
The first attempt to address the uniformity problem resulted in the CIE 1960 (u, v) uniform chromaticity scale (USC) diagram (Figure 3). Correlated color temperature was originally calculated in the CIE 1960 (u, v) UCS.
It was later discovered that the CIE 1960 (u, v) USC diagram also was not uniform. To improve uniformity the v-axis was scaled by 1.5, resulting in the CIE 1976 (u’, v’) UCS diagram shown in Figure 4. As the most uniform UCS diagram, CIE 1976 (u’, v’) is the one recommended for use when calculating or evaluating color differences, not CIE 1931 (x, y).
The definition of correlated color temperature originally used CIE 1960 (u, v). However, since that diagram is no longer recommended for any purpose by the CIE, we use CIE 1976 (u’, v’) but scale it back to CIE 1960 (u, v). This is described as CIE 1976 (u’, 2/3 v’).
The CIE’s 2014 recommendation mentioned earlier replaced MacAdam ellipses with a circle in the CIE 1976 (u’, v’) UCS. A rough rule of thumb is that one MacAdam ellipse corresponds to a circle with a radius of 0.0011. Unfortunately, it doesn’t seem that any manufacturers have made this transition.
So, our industry is in a situation where we commonly use a 90 year old first generation diagram that was replaced 61 years ago. We calculate CCT in a third generation chromaticity diagram that is 45 years old but tweek the math to refer back to a second generation 61 year old diagram. It’s crazy! No other industry uses a system this convoluted.
Why am I mentioning this? I was recently reminded of a paper that was presented at last August’s IES Annual Conference. Presented by Michael Royer of Pacific Northwest National Laboratory, it proposed using the latest color science to make a fresh start with a single new chromaticity diagram that is very similar to CIE 1976 (u’, v’) where we would calculate CCT, the color temperature bins for LEDs, color differences and the rest. IES members can access the archived presentation after logging in to the IES website.
Full disclosure, I’m on the IES Task Group that developed this new system. The Task Group is made up of people in academia, design, manufacturing and research from three countries. We’ve refined our work since August and expect to publish these refinements soon. I encourage all of you to look for and learn about this proposal, to attend seminars when available, and to weigh in on this topic. Would our industry benefit from moving to a unified chromaticity system? Is this the right one? How do we educate specifiers and manufacturers? How do we phase in a new system? We can all have a voice in bringing the science we rely on into the 21st Century.
CIE. (2014). TN 001:2014 Chromaticity Difference Specification for Light Sources. Vienna: International Commission on Illumination.
CIE. (2018). CIE 015:2018 Colorimetry, 4th Edition. Vienna: International Commission on Illumination.
MacAdam, D. (1942). Visual Sensitivities to Color Differences in Daylight. Journal of the Optical Society of America, 32(5), 247-274.
Royer, M. et. al. (2020). Improved System for Evaluating and Specifying the Chromaticity of Light Sources. In: Illuminating Engineering Society Annual Conference 2020.
For months I’ve been having conversations with friends and colleagues in the arts about our impending loss. As the world of live entertainment remains shuttered the questions are clear: What arts organizations are we going to lose this time? What entertainment professionals – performers, directors, designers, musicians, dancers, technicians and all of the rest – are we going to lose because they simply cannot wait for work to return? How many are going to leave their calling and turn to another career simply because they have to do something else to put food on the table?
On Saturday an article in the New York Times gave us a glimpse of the answer.
During the quarter ending in September, when the overallunemployment rate averaged 8.5 percent, 52 percent of actors, 55 percent of dancers and 27 percent of musicians were out of work, according to the National Endowment for the Arts. By comparison, the jobless rate was 27 percent for waiters; 19 percent for cooks; and about 13 percent for retail salespeople over the same period.
Real people are suffering real harm and the president and the republican party have been uninterested since Day 1. One of my friends, a Broadway stagehand, is now working in the stock room at Williams Sonoma. Another, a production manager, is taking well over $1,000 per month out of his retirement accounts to keep his growing debt manageable. A third, a designer, has become a house husband, living off of his spouse who (thankfully) is still employed.
“My fear is we’re not just losing jobs, we’re losing careers,” said Adam Krauthamer, president of Local 802 of the American Federation of Musicians in New York. He said 95 percent of the local’s 7,000 members are not working on a regular basis because of the mandated shutdown. “It will create a great cultural depression,” he said.
While the president has finally signed the relief bill, the break in benefits will be a burden to many. More importantly, giving $600 to people who are already employed doesn’t help those who aren’t. Targeted relief to those who need it most would have been a much smarter response.
The performing arts are in a coma. No one knows when they will receive some sort of life support. If you are able, consider making an end of year donation to one of these worthy charities.
Actors Fundcurrently has a $50,000 match offer, doubling your gift! Founded in 1882, The Actors Fund is a national human services organization here to meet the needs of our entertainment community with a unique understanding of the challenges involved in a life in the arts. Services include emergency financial assistance, affordable housing, health care and insurance counseling, senior care, secondary career development and more.
Behind The Scenesprovides financial assistance to entertainment technology professionals in need due to serious illness or injury.
Broadway Cares/Equity Fights AIDSfunding supports AIDS relief organizations, national disaster relief, food service and meal delivery programs, research initiatives, emergency assistance, and more. This year, BC/EFA also established the COVID-19 Emergency Assistance Fund, administered by The Actors Fund, to help entertainment professionals facing health care crises and other immediate needs due to the coronavirus.
If you’re looking for other options, Playbillhas list of 40 theatre-related charities you can consider.
Two weeks ago the Metropolitan Opera announced that it was cancelling its entire 2020/21 season. Today, the Broadway League announced that Broadway performances would remain suspended through the end of May 2021. Charlotte St. Martin, President of the Broadway League, said,
With nearly 97,000 workers who rely on Broadway for their livelihood and an annual economic impact of $14.8 billion to the city, our membership is committed to re-opening as soon as conditions permit us to do so. We are working tirelessly with multiple partners on sustaining the industry once we raise our curtains again
The announcement effectively cancels the 2020/21 Broadway season leaving a question about what will happen with next year’s Tony Awards. More importantly is the question of what will happen to all of the artists and technicians who work on Broadway whose 39 weeks of extended unemployment benefits will run out in December of this year.
If you care about the future of the performing arts in America, contact your Senator and Representative and urge them to pass The Save Our Stages Act (S. 4258) which has been trapped in committee in the Senate since July 7th. Introduced by Senators John Cornyn (R-TX) and Amy Klobuchar (D-MN), it provides vital support for performing arts venues that have lost nearly 100% of their revenue since the pandemic began in March. The companion bill in the House (H.R. 7806) is led by Representatives Peter Welch (D-VT) and Roger Williams (R-TX).