Fixing CRI, But Not Really

A couple of weeks ago the Global Lighting Association (GLA) published Application of CIE 13.3-1995 with Associated CRI-based Color Rendition Properties.  It proposes TM-30 like metrics to supplement CRI Ra.  Specifically, it proposes a color gamut index, Ga, that is similar to TM-30’s Rg and a set of chroma indices, Ci, similar to TM-30’s Rch,hj.  At first glance I can see some specifiers getting excited about this.  Since it’s based on CRI it’s already somewhat familiar so it should be easier to learn.  But…

The first part is the problem – it’s based on CRI, which has well known and well documented problems and shortcomings.  As described in The Lighting Handbook, 10thEd.and IES DG-1 Color and Illumination, they include:

Averaging the Color Shifts. CRI is computed by averaging the color shifts of the eight color samples.  A light source can render one sample very poorly and still achieve an acceptable score.  The Chroma Indices attempt to resolve this, but there’s a problem with the eight color samples, which is next on our list.

Test Color Samples. The eight color samples are all of moderate saturation, so saturated colors can be rendered poorly even when CRI is high.  More importantly, the eight color samples are A) not based on any real-world objects B) don’t adequately cover the visible spectrum.  The latter is significant because it means that some wavelengths play an outsized role in determining CRI.  Manufacturers can use this to optimize (or cheat) their spectrum to achieve a higher CRI than visual inspection would warrant.  This is why TM-30 uses 99 color samples drawn from real world objects.

Color Space.  CRI is calculated in the CIE 1964 color space, which is no longer recommended for any other use because it is outdated.

Penalties for all Chromaticity Shifts.  As a fidelity metric, CRI penalizes all chromaticity shifts even though research has shown that certain increases in chroma are preferred.  Again, it seems that Ci is intended to address this, but it doesn’t resolve the other problems with CRI. 

Chromatic Adaptation. The chromatic adaptation transform used in CRI has been shown to perform poorly and is no longer recommended for any application.

CRI served the industry (relatively) well, but its time is over.  Layering new calculations on top of CRI’s flawed foundation doesn’t make it better. I know TM-30 can be tough.  But it works.  It tells us what we want to know at the level of detail we need for a given project, and it’s accurate.  The IES has moved on and the CIE seems to be leaning in that direction as well.  So should you!

NYT Talks Lighting Design, But Not With Lighting Designers

Sometimes the New York Times is oblivious and yesterday was one of them.  In an article titled Lighting a Room, Simplified the author wrote about the importance of lighting in the home.  In preparing the article, she spoke to and quoted four interior designers, one fixture manufacturers and  one professional lighting designer.  In addition, all eight of the photos in the article are taken during the day, so they’re nice illustrations of the use of windows and daylight in residential interiors but terrible illustrations of electric lighting, which is the topic of the article.  They seem to  be marketing photos for particular lighting fixtures, not examples of good lighting.

It’s too bad.  There are plenty of lighting designers who would have gladly shared their expertise and their work with the public if asked.  Unfortunately, this article is a reflection of the public’s (and the author’s) lack of awareness of the contribution good lighting, and therefore a good lighting designer, can make to a residential of commercial project.

Lighting doesn’t just come with a building.  Most interior designers and architect receive little or no training or education in lighting design when they’re in school.  Yes, some do have an affinity for lighting and can create beautiful work despite their lack of training.  However, the best lighting design is most likely to come from the best trained people – professional lighting designers.  If you are looking, one place to start is the IALD’s web site and the Find A Lighting Designer tool on the home page.








IES Releases Ready Reference App

For many years the IES Ready Reference was on the desk of every lighting designer, and we were all baffled when they stopped publishing it.  Great news, it’s back!  This time as an app for your phone or tablet that’s available in the Apple App Store and Google Play.  According to the IES, the app provides:  

  • Core lighting knowledge, including values from illuminance tables
  • General knowledge information, assembled from The Lighting Handbook, 10th Edition and IES standards
  • Simple calculators for quick and easy basic lighting and energy and economic calculations
  • A search feature allowing you to find the information you want

Download it from the Apple App Store or Google Play.








TM-30 and Daylight

An architect recently emailed me asking if it was possible to use TM-30 metrics with daylight.  My short answer was something like, “I suppose you could, but why would you?”

The long answer is that all of the TM-30 measurements (Rf, Rg, the 16 chroma shifts, the 16 hue shifts) are relative – comparing the light source in question with the reference light source.  With daylight, you’d be comparing the daylight SPD you captured at a moment in time with the CIE definition of daylight at the same CCT.  On an average day I doubt that any of the measurements would deviate from 100 by more than a couple of points.  So, using TM-30 (or CRI Ra) is like measuring a ruler with another ruler.  You’re essentially comparing one thing to a definition of itself.








Specifying Color Quality With TM-30

By now most of us have attended one or more seminars or webinars about IES TM-30 and understand that it is a method of measuring various color rendering properties of a light source and reporting those measurements.  The thing that’s been missing is a recommended set of values that set minimums, maximums and/or tolerances for the various measurements.  This has been true for two reasons.  First, TM-30 is a method and as such was never intended to set recommended values.  The second is that while the science behind TM-30 is solid, the science doesn’t offer any predictions of acceptability.

Good news!  After almost three years of research and tests around the world we’re much closer to establishing a set of recommended values.  At this year’s IES Annual Conference in Boston, Tony Esposito, Kevin Houser, Michael Royer and I will be presenting the seminar “Specifying Color Quality With TM-30”  The description of the seminar is, “This presentation will discuss several research projects which have used the IES TM-30 color rendition framework, and whose results have been used to develop various specification criteria. We will discuss UFC 4-510-01, The Department of Defense Unified Facilities Criteria for Military Medical Facilities, which has already implemented IES TM-30-15 specification criteria.”

During the seminar we’ll review some TM-30 basics, look at several research projects that are helping to establish TM-30 thresholds, and review how to use the TM-30 calculator.  Don’t miss it!








International Day of Light 2018

Today, May 16th, is the International Day of Light 2018.  It began in 2015 when the U.N. declared  The International Year of Light and Light-based Technologies.  Today, the International Day of Light is

a 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. The broad theme of light will allow many different sectors of society worldwide to participate in activities that demonstrates how science, technology, art and culture can help achieve the goals of UNESCO – education, equality, and peace.

There are events around the globe related to the theme of light.  If you’re interested you can check the web site, and the sites of organizations such as IALD and IES.