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.

Tony and I Talk Color Rendering

Podcast Album Cover

In September at ArchLIGHT Summit, Tony Esposito and I gave a series of demonstrations on the spectral flexibility of LEDs and the possibilities they present with regard to color rendering.  While there we spoke to Sam Koerbel on his LytePod podcast about the basics of the new measures introduced in Annex E, and discuss why TM-30’s multi-dimensional approach to quantifying color preference is superior to the old-standby in the industry: CRI.  Our discussion is now available.  Give it a listen.

The Strength of TM-30

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.

Alternating between light sources with Rf 70, Rg 94 and Rf 70 Rg 111

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!

New TM-30 Tutorial Available

Many of us on the IES Color Committee, myself included, have written and spoken about TM-30 and how to use it. I’ve written posts on this blog (click on the color rendering tag to see them all), authored articles, spoken at IES Annual Conferences, given webinars to architects and lighting designers, and assisted manufacturers in adding TM-30 data to their cut sheets. Despite our efforts, and those of others, TM-30 is still not as well understood and broadly implemented as it could be.

A recent issue of Leukos featured an excellent tutorial by Michael Royer of Pacific Northwest National Laboratory. In it, he describes the development of TM-30, color rendering fundamentals, the workings of the TM-30 calculation framework, TM-30 measures and their meaning, and more. That article is now available on the US Department of Energy’s website here. Anyone who’s unsure about TM-30 will find it immensely useful.

On a related note, many members of the IES Color Committee, myself included, can make themselves available to answer questions or present webinars to architects, interior designers, lighting designers, electrical engineers, sales reps, and manufacturers. If you’re interested, use the Contact Jason Livingston link above to send me a message. If I’m not available or the right person for your organization I’ll find someone who is.

What is the Reference Illuminant?

Over the past few months I’ve had a manufacturer, a sales rep, and a lighting designer all tell me they think CRI compares a light source to daylight.  When I tried to correct one of them the reply was an acknowledgment that an incandescent source is normally used, but daylight can be used, too. Given that the lighting industry has been using CRI since 1965, all three should have known better.  On the assumption that they’re not alone in their misunderstanding, let’s talk about reference light sources.

The International Commission on Illumination (CIE for Commission Internationale de l’Eclairage) and the Illuminating Engineering Society (IES) both define color rendering as, “The effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant.”  In other words, we evaluate the color rendering of a given light source by comparing it to another light source.  The other light source is called the reference illuminant.  

In 1965 the CIE published CIE 13 Method of Measuring and Specifying Colour Rendering Properties of Light Sources.  The current version is CIE 13.3-1995.  Its General Color Rendering Index, Ra, is usually referred to as CRI. CIE 13.3 says, “the reference illuminant for light sources with correlated colour temperatures below 5000 K shall be a Planckian radiator, and from 5000 K one of a series of spectral power distributions of phases of daylight.”  

So, the reference illuminant must have the same color temperature or correlated color temperature (CCT) as the light source being tested. For all light sources with a CCT below 5000 K we use the spectrum of a Plankian, or blackbody, radiator.  For all light sources with a CCT of 5000 K or above we use a CIE model of daylight, again at the same CCT as the light source we’re testing.

Regular readers of this blog know that I’m not a fan of CRI, greatly preferring the increased accuracy and depth of information provided by ANSI/IES TM-30 IES Method for Evaluating Light Source Color Rendition.  What about TM-30’s reference light source?  It’s nearly the same.  For CCTs of 4000 K and below it’s a Plankian radiator.  For CCTs of 5000 K and above, it’s the CIE model of daylight.  TM-30 avoids CRI’s sudden jump between reference illuminants by using a graduated blend of Plankian radiator and daylight over the range of 4001 to 4999 K. 

CIE 224 Color Fidelity Index for Accurate Scientific Use is identical to TM-30’s Fidelity Index (Rf) and uses the same reference light sources.

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.

Standard 189.1 Now Includes TM-30 Requirements

Yesterday an addendum to ANSI/ASHRAE/ICC/USGBC/IES Standard 189.1-2017 Standard for the Design of High-Performance Green Buildings was published. The addendum makes changes to Section 8.3.5, which covers lighting. One of the biggest changes is to add TM-30 color rendition criteria to the section on Indoor Lighting Quality. Here’s the relevant text:

8.3.5.3 Color Rendition. At least 95% of lighting power of nominally white lighting within each enclosed space shall be provided by luminaires that meet the following criteria at full light output in accordance with IES-TM-30, Annex E, P2 and F3:
1. Rf of at least 85
2. Rf,h1 of at least 85
3. Rg of at least 92
4. Rcs,h1 of at least -7% but no greater than +19%

Nominally white lighting is lighting that has chromaticity within the basic or extended nominal color correlated temperature (CCT) specifications of ANSI C78.377.

Where a lighting system is capable of changing its spectrum, it shall be capable of meeting the color rendition requirements within each nominal CCT of 2700 K, 3500 K, 4000 K, and 5000 K, as defined in ANSI C78.377, that the system is capable of delivering.

I hope that this is going to put more pressure on manufacturers to improve the color rendering of their luminaires as measured by TM-30, not CRI, and to provide TM-30 information on their cut sheets. If not, they’ll risk not being considered on projects that have TM-30 requirements.

Using TM-30 to Improve Your Lighting Designs

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.

The IES Forum for Illumination Research, Engineering, and Science (FIRES) has an article I wrote with Michael Royer and Tony Esposito explaining the Annexes and how to use the information in Annex E.  Here’s the link: Using TM-30 to Improve Your Lighting Design – Illuminating Engineering Society

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.