Designing Beyond Fidelity

I recently began a project that includes about 8,000 SF of office space that is completely without windows or skylights.  I’ve renovated spaces like this before, and the common complaint from occupants was a disconnect from daylight, weather, and the way they indicate the passage of time.  On this project, I determined that the most appropriate solution was to use a light source that rendered colors in a way that is highly preferred to make the spaces more pleasant to occupy and use.

Of course, as a designer who is very knowledgable about color rendering issues and is a TM-30 advocate, I know two things.  First, highly preferred is not high fidelity.  People prefer a light source that slightly increases the saturation of object colors (especially reds) over a high fidelity source.  Second, TM-30’s Annex E provides specifiers with ranges for certain TM-30 measurements that allow us to accurately specify highly preferred light sources.

The task seemed simple enough.  Forget about fidelity and find a fixture/LED combination with a spectrum designed for preference, i.e. a light source that meets the TM-30 Annex E specification for a highly preferred (aka P1) light source.  After all, we’ve had TM-30 for seven years now, and Annex E for four years.  Surely, by now LED manufacturers have introduced products that meet color rendering goals other than fidelity, right?  Who wouldn’t see that as a huge marketing opportunity?  And surely fixture manufacturers would offer specifiers that LED, again to differentiate their products from the many, many, many similar products from other manufacturers…right?

Alas, the answer is, “No.”  One member of the IES Color Committee shared with me a database of over 1,000 LED products, their SPDs, and their various TM-30 measurements, including the Annex E Preference Design Intent.  Of those, there are a generous handful of retrofit lamps, most of them by Soraa and Cree, that meet the P1 specification, but only one LED in commercially available linear LED fixtures – Focal Point’s Preferred Light series.  That’s it!

Fortunately, this project is for a private firm so I don’t have to worry about developing a three-name or performance spec.  Otherwise, I would have to give up on a preferred spectrum and default to high fidelity not because it would be appropriate for the project but simply because there are more options.

I’ve mentioned fidelity and preference.  You might be asking if there are other color rendering goals.  The answer is, “Yes.”  Other color rendering design goals, with brief explanations, include:

Preference.  Light distorts object colors with slight increases in saturation, especially reds, in a way that is preferred over the reference light source (that is, preferred over high fidelity).   This might be the goal in an expensive restaurant where you want to emphasize the beautiful colors of the food, people, and interior design.

Vividness.  Light renders object colors as more or less vivid, or saturated, than the reference light source. Vividness is different from Preference in the degree of distorted saturation and the design intent – making colors pop, not making colors more attractive.  This might be the goal in the Skittles store in Times Square where you want the colors to leap out at people.  

Naturalness. Light renders object colors as expected, which, surprisingly, is usually not the same as fidelity.  This might be the color rendering goal in a grocery store where you want the food to look ripe and appetizing.

Discrimination.  Light renders object colors so they can be appropriately sorted. This might be the goal in a facility where even slight color variations must be detected.

Specifiers are captives of manufacturers.  We can have design goals oriented toward the needs of the users and the success of the project, but manufacturers only want to sell us fidelity, the same way they’ve been selling us fidelity since CRI was introduced in 1965.  For 50 years we only had a hammer (CRI) so all problems were nails (fidelity).  TM-30 changed that and it’s time for manufacturers to catch up.

Manufacturers Don’t Understand Color Rendering

I attended LEDucation in New York City this week.  While there I spoke to over two dozen manufacturers, none of whom understood color rendering beyond the (partially accurate) belief that higher CRI is better.  My conversations when like this.

Lighting Salesperson: “Our color rendering is great.  Our CRI is over 90 and our R9 is over 50.”

Me: “CRI measures color fidelity.  What if my goals are something else?”

Lighting Salesperson: “…”

or

Lighting Salesperson: “Our color rendering is great.  Our CRI is over 90 and our R9 is over 50.”

Me: “CRI has inaccuracies that have been known for decades while TM-30 is the most accurate and up to date system.  If color fidelity is important to you, why aren’t you using TM-30’s Rf?”

Lighting Salesperson: “Well, lighting designers don’t understand TM-30.”

Me: “Oh, I think many of them do.  But, even if they don’t, don’t you want to be sure that your color rendering claims are true?  Couldn’t you educate designers about TM-30?  The IES Color Committee will help.”

Lighting Salesperson: “…”

So, (big sigh, big eye roll) let’s go over this again.  If we think of CIE 13.3-1995 Method of Measuring and Specifying Colour Rendering Properties of Light Sources, aka CRI, as a technology, then it’s a technology from 1965 which is when the first version was published.  In 1965 Lyndon Johnson was president, Bonanza was the most popular TV show, Wooly Bully by Sam the Sham and The Pharaohs was the most popular song, and the Chevrolet Impala (Jet Smooth Ride!) was the most popular car.  CRI is O-L-D.

As with any other technology that is 57 years old,  the science has advanced.  Unfortunately, CRI has not. There were two minor corrections, the most recent in 1995, but they did little to fix at least a half dozen errors and inaccuracies that have been well documented for decades.  The CIE basically admitted that when, in 2017, they published CIE 224 Colour Fidelity Index for Accurate Scientific Use, which is TM-30’s Rf measure of fidelity.  Why publish 224 and not withdraw CRI?  Why have one measure for accurate scientific use and one for (inaccurate?) general use? The CIE requires unanimous votes for any action to be approved.  I’m told by reliable sources who were in the room that one global lamp manufacturer has been resisting updating or replacing CRI for decades, and that one manufacturer has held up progress or change.

So, CRI is has known inaccuracies resulting from a combination of outdated internal calculations along with other limitations.  Meanwhile, TM-30 is known to be the most accurate measure of fidelity.  If fidelity is your concern, Rf is the measurement you want to use.

What about concerns other than fidelity?  When TM-30 was published in 2015 there wasn’t evidence it could be used for purposes other than fidelity.  However, by 2018 studies provided ample evidence that TM-30 measures could also be used to evaluate light sources for preference and vividness.  The studies are summarized in TM-30’s Annex F, and recommendations based on those studies are in Annex E (yes, that seems backwards, sorry).  Here’s an explanation of all three color rendering goals. (Oh, and TM-30 is still a free download from the IES!)

I think preference is an incredibly interesting color rendering goal.  Color preference means that the light source in question renders colors differently than the reference light source (and therefore has a lower fidelity) but does so in a way that is preferred by most people (usually by slightly increasing the saturation of colors, especially red).  Color preference is usually my color rendering goals in spaces, such as hospitality, where aesthetics are the primary concern.

Manufacturers don’t get it. Designers do, and we have to demand that they educate themselves so they can provide us with the tools we need.

Updating the CCT Calculation

As I noted in Chapter 9 of the 2nd edition of Designing with Light, we calculate color temperature, correlated color temperature, and distance from the Plankian locus in a perverse way.  The calculations are performed in the CIE 1960 (u, v) chromaticity diagram (which is why distance from the Plankian locus is Duv).  However, since 1960 (u, v) is obsolete, we perform the calculation using CIE 1976 (u’, v’) chromaticity diagram, but then scale the v’ axis by .66 so that we’re using 1976 (u’, ⅔ v’) which is 1960 (u, v).

To complicate things, to present information graphically, most manufacturers transpose these calculations to the 1931 (x, y) chromaticity diagram, resulting in the industry using 2 ½  chromaticity diagrams for various calculations and illustrations.  Unfortunately, they also use 1931 (x, y) to illustrate the gamut of multi-colored luminaires even though it isn’t uniform, making the illustration of questionable value (they should be using CIE 1976 (u’, v’), which is perceptually uniform).

In a counter to this fragmented system, yesterday Leukos published a research article called Improved Method for Evaluating and Specifying the Chromaticity of Light Sources.  Among other proposed improvements to how we perform chromaticity related calculations, it introduces a new uniform chromaticity scale (UCS) diagram with coordinates (s, t), a measure of correlated color temperature (CCTst), and a measure of distance from the Planckian locus (Dst).  Importantly, it makes all chromaticity calculations in a single chromaticity diagram instead of the 2 ½ diagrams we use today.  It’s heavy on the science, but is an important step in fixing our current system.

Designers Thinking About Light – IES Vancouver Section

On February 24th I’m giving an online presentation called Designers Thinking About Light to the Vancouver section of the IES.  I’ll be talking about how lighting designers think about light as an artistic medium.  The presentation will include some ideas you probably know, as well as some approaches that will be new.  To register, visit the IES Vancouver Section web site.

The Limits of a ‘Standard’ Observer

I tell my students that we’re lighting designers not scientists, but that it’s good to understand some of the science that underpins our work.  This is especially true when the science is out of date and produces results that don’t necessarily agree with our vision and/or perception.  It’s frustrating and amazing to me that as individuals we’d never agree to use a broadcast only TV and give up our modern cable and internet channels. We’d never agree to use a flip phone and miss out on all of the upgrades and improvements that have been developed over the years. Yet as an industry we seem perfectly happy to continue to use 75+ year old technology with known flaws when we calculate color rendering, measure brightness, plot chromaticity in color spaces, etc.  Our industry doesn’t seem interested in “upgrading” to get the latest features like less metameric mismatch and measurements that better align with our vision and perception. But, I continue to shout into the void about these things.

One of these topics is the standard observer. This article, online and in the current issue of LD+A, looks at the problems that can arise from continuing to rely on the 1931 standard observer, and not “upgrading” to the 1964 or 2015 standard observers.

TM-30 at ArchLIGHT Summit 2021

My colleague Tony Esposito and I will be giving a new TM-30 seminar and demonstration at ArchLIGHT Summit 2021 in Dallas on September 21st and 22nd. We’re working on a new, and we hope more attendee friendly, presentation and an all new set of demonstrations to explain TM-30s Annex E specifications. The demo will include, for the first time, live models of different ethnicities so attendees can evaluate the impact of of the specifications on skin tone. I hope to see you there!

TM-30 Is Not Too Hard To Learn!

Recently, a well-known lighting designer gave a presentation at a well-known lighting conference. During the Q&A he was asked his opinion of TM-30 and replied that it was too hard so he just specified CRI>90. At the risk of sounding like a jerk I have to say that maybe it was too hard for him, but it’s not too hard for most of us. Here is a brief list of new things lighting designers have had to learn over the years.

  • The introduction and transition to electronic ballasts and transformers meant that we had to learn about reverse phase dimming and control protocols.
  • The T5 lamp meant we had to change our layout patterns to accommodate lamps that weren’t standard 2’, 4’, and 8’ lengths.
  • Metal Halide lamps, especially PARs, meant that in exchange for energy savings we had to learn about the color rendering of a new type of lamp, and give up dimming.
  • Daylight harvesting and daylight responsive designs meant we had to learn about daylight zones, photosensors, and daylight harvesting control systems.
  • White LEDs meant we had to learn about another light source and its specific pros and cons, including different color rendering properties due to its SPD.
  • Circadian lighting means we are all in the process of learning how and when to apply the most current scientific evidence to certain project types.  Since the science is constantly advancing on this topic, we must be aware and continue to educate ourselves.
  • Regularly updated energy conservation codes mean that as we begin to memorize the lower LPDs and changes to control and daylighting requirements, we have to relearn that information because it changes every three years.
  • Most recently, we’re supposed to enthusiastically embrace IoT, adding new hardware and controls to our lighting control systems.

There is a ton of TM-30 educational material available, including posts on this blog here, here, here, here, here, and here. There’s this article on the IES’s FIRES Forum, and this page on the Department of Energy web site. Manufacturers are also providing education including DMF Lighting, Soraa, Premier Lighting, Alphabet, and Lighting Services Inc. Then there are the articles in trade magazines and sites such as Lux Review and Architect Magazine, not to mention many articles in Lighting Design and Application and Leukos (no links because they’re behind the IES login). In addition, there have been presentations at other conferences (some given by me) at the IES Annual Conference, LightFair, and LEDucation.

If that’s not enough for you, let me know. I have a presentation approved for one AIA HSW LU, so if you’re architectural firm wants to learn more let’s set up a presentation. Ditto for lighting design firms and teachers of lighting. If I’m not available there are a half dozen others on the IES Color Committee who regularly give TM-30 presentations. You can learn TM-30. I’m here to help.

IES RP-16 is Now IES LS-1

The Illuminating Engineering Society’s Recommended Practice 16 Nomenclature and Definitions for Illuminating Engineering (aka RP-16) has long been one of the two reference sources for the definition of lighting related words and phrases – the other being the CIE International Lighting Vocabulary (ILV).

As part of the IES converting all of their publications to an online library format, some publications have been given a new designation. RP-16 is now Lighting Science 1 (LS-1) and is at this link. Bookmark it now!

CIE Position Statement on the use of UV-C

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.

Read the full position statement.








A Look at Bridgelux’s Average Spectral Difference Metric

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.

J. Holm et al., “A Cinematographic Spectral Similarity Index,” SMPTE 2016 Annual Technical Conference and Exhibition, Los Angeles, CA, 2016, pp. 1-36, doi: 10.5594/M001680. Also: https://www.oscars.org/science-technology/projects/spectral-similarity-index-ssi

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.