Category: Lighting Profession

CCT Doesn’t Predict Circadian Impact

Two of my IES Color Committee friends and colleagues, Tony Esposito and Kevin Houser, have just published a paper in Scientific Reports that looks at the common assumption that CCT can be used to assess circadian entrainment and other biological impacts of light. The assumption by many is that high CCT light contains the blue wavelengths necessary for circadian entrainment, and that assumption is emphasized in the marketing a wide range of tunable white fixtures.

Their study used a five-channel LED system in a full scale model of a room. The LEDs were used to create over 200,000 SPDs across a range of color temperatures and illuminance levels. They found that CCT alone is not an accurate predictor of the spectral content of the light. Since the three major systems used to predict “biological potency” of light – CIE melanopic Equivalent Daylight Illuminance (mel-EDI), Equivalent Melanopic Lux (EML), and Circadian Stimulus (CS) – all use spectral analysis to understand biological impact, using CCT alone is simply inadequate. High CCT may correspond to circadian response, or it may not. They conclude their paper by saying

The lighting industry is experiencing rapid transformation as we expand our awareness of the non-visual impacts of light on humans. It is pertinent that we develop measures, methods, and strategies for implementing architectural lighting solutions that support these non-visual impacts. To do so, we need accurate and predictive measures of the biological potency of light that are based on sound science. In this study, we have argued that CCT is conceptually inappropriate for this purpose and performed a numerical analysis demonstrating that significant variation in circadian stimulus and melanopic equivalent daylight illuminance exists at any fixed CCT and photopic illuminance, making CCT an inappropriate proxy of those measures. Using CCT as a proxy for the biological potency of light cannot be justified.

Understanding that CCT doesn’t correspond with biological impact, it becomes important that designers understand the three systems and push manufacturers to begin providing the relevant information.

California Bans Fluorescent Lamps

Last week California joined Vermont and the European Union in enacting a ban on fluorescent lamps.  The California ban covers:

  • Screw or bayonet base CFLs beginning January 1, 2024
  • Pin-based CFLs beginning January 1, 2025
  • Linear fluorescent lamps (aka fluorescent tubes) beginning January 1, 2025

The ban isn’t complete because there are some specialty fluorescents that are not included, such as those used for copiers and scanners, disinfection, sunlamps for tanning, and specialized lamps for medical purposes.  However, it does apply to:

  • CFLs of all tube diameters and all tube lengths, including PL, spiral, twin tube, triple tube, 2D, U-bend, and circular
  • Linear fluorescents including:
    • single-pin, two-pin, and recessed double contact
    • all tube diameters, including T5, T8, T10, and T12
    • all tube lengths from 6″ to 8′
    • all lamp shapes, including U-bend and circular

Over the next few years hundreds of thousands, probably millions, of fixtures will need to be replaced or, if possible, converted with LED retrofit lamps.  From the perspective of efficiency and quality of light replacement is certainly preferred, but it won’t be cheap.  It’s not clear if California or utilities will offer any sort of financing to make the change.

You can download the law here.

ArchLIGHT Summit and Get A Grip On Lighting

Next month I’ll be at ArchLIGHT Summit in Dallas.  Together with my IES Color Committee co-chair Tony Esposito, we’ll be giving several presentations on how designers can make better use of TM-30 by integrating it into their workflow.  In anticipation of our ArchLIGHT Summit presentation we were interviewed on Get A Grip On Lighting, where we talked about TM-30, color perception, and color rendering, among other things.  You can watch the interview on their web site, or below.

 

Don’t Call Me A “Creative”

I was recently referred to as a “creative” and the person who said it was surprised when I asked not to be called that.  Here’s why I hate that word used as a noun.

In other industries the training, talent, and roll of individuals is recognized.  In finance, for example, there are bank tellers, stock brokers, analysts, hedge fund managers, etc.  While we might say they all work in the financial industry, we don’t call them “financials” or “moneys”.  We describe each person’s role using the name of their distinct profession.  Kayla is a financial analyst, not a “money”.

Likewise, in medicine there are nurses, doctors, surgeons, EMTs, etc.  We might collect all of their expertise when we refer to the medical or health care field, but we don’t call the individuals “medicals”.  Again, we describe each person’s distinct role or profession.  Alex is a registered nurse, not a “health”.

I work in a creative profession, but I’m a lighting designer not a “creative”.  I’m not a poet, choreographer, photographer, or web site designer.  I find it lazy and dismissive to lump all of us into one category and call us “creatives” as though we’re interchangeable, without regard to the education and skills of our very distinct professions.  You don’t want a web site designer lighting your building, or a choreographer making your web site.  To me, calling us all “creatives” disregards and degrades our unique abilities and contributions, essentially saying that what we do isn’t worth recognizing or naming.

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.

IES Publishes “Standards Toolbox”

The IES has added a Standards Toolbox to their web site that features an online TM-30 and TM-21 (projected luminous flux maintenance, i.e. LED lifetime projections) calculators, an interactive illuminance selector (for subscribers to the IES Online Library), and an IES Reference Retriever where members can access all of the documents, articles, and papers referenced in various IES documents.

Of course, I’m most excited about the TM-30 calculator which imports and exports spectral data and reports in a variety of formats and increments, and will always be the most up-to-date version.  As a bonus, the calculator’s code is also available for download on GitHub, which may be of special interest to manufacturers who want to bring calculations in house instead of doing them online.

The TM-30 calculator includes CIE S026 Alpha-Opic calculations (CIE S 026:2018. System for Metrology of Optical Radiation for ipRGC-Influenced Responses to Light) and output, and is expected to include additional spectral calculations in the future.

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.