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Designing Light

Designing Light

The companion blog to the book Designing With Light

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Welcome to the companion web site for Jason Livingston's Designing With Light: The Art, Science, and Practice of Architectural Lighting Design.

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You are browsing the Blog for Color.

R.I.P. CRI

October 16, 2017 in Calculations, Color, Design, Lamps, Lighting Profession

It’s been a little over two years since the IES released TM-30-15 IES Method for Evaluating Light Source Color Rendition.  In that time TM-30 has seen growing support in the industry and a growing body of evidence for its accuracy and usefulness.  We’ve nearly reached the moment when we can all agree that it’s time to retire CRI and fully adopt a modern, accurate system of measuring and describing the color rendering of light sources.  What’s wrong with CRI?  Quite a bit, so if you’re not up to date on the issue here’s an overview.

In 1948 The CIE first recommended a color rendering index based on a method developed in 1937.  The 1937 method is a fidelity metric (that is, it compares a test light source to a reference light source) that divides the spectrum into eight bands and compares each band to a full spectrum radiator.  In 1965 the CIE finally adopted CIE 13-1965 Recommended method of measuring and specifying color rendering properties of light sources, based on a test color sample method, what today we call CRI Ra or just CRI.  From the start it was apparent that there were problems.  In 1967 a committee was established to correct for adaptive color shift.  Other problems were uncovered, and in 1974 a formal update was published.  Errors were uncovered in the 1974 edition, resulting in a third version in 1994, which is the version we use today.

So far, so good.  Errors are discovered in the method used and are eventually corrected, so what’s the fuss?  The fuss is that the corrections were minor compared to the scope of the errors, and 23 years after the last correction we still don’t have an accurate, up to date system.  In the early 1990s a proposal to update the formula and test color samples failed to gain consensus.  Two subsequent attempts to improve the metric also closed without adoption.  The current problems, as described in the 2011 IES Lighting Handbook, 10th Edition include:

  • Averaging the color shifts of the eight test colors says nothing about the rendering of any single sample.  A large error in one color can be masked by accurate rendering of the other samples.
  • The test color samples are all of moderate saturation so the index doesn’t reveal color shifts in saturated colors.  In addition, the test colors are not evenly distributed through the color space or the spectrum, so light source spectra can be engineered to score higher than visual observation would indicate.
  • The color space used, the 1964 UCS chromaticity diagram, is no longer recommended for any other use.
  • All chroma shifts are penalized, even though research shows that moderately increasing chroma is desirable in many applications.
  • The chromatic adaptation used has been shown to perform poorly and is no longer recommended for any other use.
  • A single number index gives no information about the direction or extent of color shift for any particular color or color range.

Why haven’t these problems been corrected in the past 23 years?  I’m told that there are two issues.  The small issue is that competing scientific interests on the committee advocate new metrics that they’ve developed as a replacement or supplement to CRI.  The larger problem is that manufacturers on the committee don’t want to see any changes that would reduce the CRI of any of their lamps.  From their perspective, it’s better to have a high score on an inaccurate test than a low score on an accurate one.  It seems that internal politics has been preventing updates, corrections, and improvements.

Although many other color rendering metrics have been proposed over the years, none has been adopted by CIE, which has the most significant voice on this issue.  The result is that the sole internationally accepted metric, which has also been written into product specifications and into codes, is CRI.  That began to change in 2015 with the introduction of TM-30. I’ll have more to say about TM-30 in future posts, but for now let’s agree that CRI Ra is broken and CIE is in no hurry to fix it.  A better system exists, and our industry should adopt it.

Tags: color rendering, CRI, TM-30
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The World Has Millions of Colors. Why Do We Only Name a Few? 

September 20, 2017 in Color, Light, Psychology, Vision

This article explains an interesting new theory on why we have names for some colors, and why colors are named in the same order for almost all languages.

Tags: Color Perception
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Understanding Color (just for fun)

August 28, 2017 in Color

A little color fun from xkcd.com.

 

Tags: Color Perception
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IES Disagrees With AMA on Night Time Outdoor Lighting

June 28, 2017 in Color, LEDs, Light

Last year the AMA issued Policy H-135.927 Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting, which recommended, among other things, that LED outdoor lighting should have a CCT of 3000 K or below.  The AMA made this recommendation thinking that lower correlated color temperatures contain less blue light, which can disrupt circadian rhythms.

Today the IES issued a Position Statement disputing that recommendation, noting that CCT

is inadequate for the purpose of evaluating possible health outcomes; and that the recommendations target only one component of light exposure (spectral composition) of what are well known and established multi-variable inputs to light dosing that affect sleep disruption, including the quantity of light at the retina of the eye and the duration of exposure to that light. A more widely accepted input to the circadian system associated with higher risk for sleep disruption and associated health concerns is increased melanopic content, which is significantly different than CCT. LED light sources can vary widely in their melanopic content for any given CCT; 3000 K LED light sources could have higher relative melanopic content than 2800 K incandescent lighting or 4000 K LED light sources, for example.

Follow the link to read the entire Position Statement.  Blue light hazard, light’s impact on circadian rhythms and overall health, and related topics are a hot area of research.  We’re learning more all the time, but we don’t yet know enough to apply circadian lighting to every situation.  Outdoor and street lighting are among the areas where research is not yet conclusive.

Tags: color rendering, LED color, Light and Health
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A New Report on LED Color Shift

June 15, 2017 in Color, LEDs, Light

Like other lighting technologies, the color or chromaticity of light emitted by an LED can shift over time.  To address the challenge of developing accurate lifetime claims, DOE, together with the Next Generation Lighting Industry Alliance, formed an industry working group, the LED Systems Reliability Consortium (LSRC).  A new LSRC report, LED Luminaire Reliability: Impact of Color Shift, focuses on chromaticity. The purpose of the new report is not to define limits for specific applications, but rather to enable a better understanding of how and why color shifts, and how that impacts reliability.  Download it and take a look.

Tags: LED color
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CIE Adopts TM-30 (sort of)

May 3, 2017 in Color, Light

The CIE has issued a statement titled “CIE 2017 Colour Fidelity Index for accurate scientific use” in which they partially adopt the Rf fidelity metric of TM-30.  Here are some of the details.

When the IES released TM-30-15 it seemed to be a wake up call for the CIE, who have understood the inaccuracies of CRI but haven’t been able to build the internal consensus to correct them.  Two CIE committees soon began  work, one on the issue of fidelity and one on other perception related issues.  The committee that worked on fidelity (TC 1-90) has decided to adopt TM-30 Rf with a few minor changes to the calculation.  They are calling this the CIE 2017 Color Fidelity Index, which will still be described as Rf, and are asking the IES to adopt the same changes to the calculation so that both Rfs are the same.

However, at this time there is no retirement date for CRI, even though they acknowledge that Rf is more accurate.  The logic is a bit twisted.  Since CRI is used for purposes other than the intended purpose, and since TM-30 doesn’t satisfy those purposes, we’re going to continue to mis-use CRI.  Meanwhile, “replacement of the CRI will be a matter of future study and discussion.”

I’ll probably have more to say once I read the entire report.  If you want to read the report yourself you can purchase it here.

Tags: color rendering, CRI, TM-30
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Design Guide for Color and Illumination

May 1, 2017 in Color, Design, Light, Lighting Profession

As the co-chair of the IES Color Committee I am delighted (pun intended) to announce the publication of the Design Guide for Color and Illumination.  The guide is the result of over five years of work by more than a dozen researchers, engineers, manufacturers, and designers from across the globe.  Here’s part of the description on the IES site.

Color can be described using concrete values such as chromaticity coordinates, spectral power distribution, or others discussed later in this guide. However, one’s response to color can be much more personal and emotional—and therefore more difficult to quantify. This guide takes the reader from basic vision and color vocabulary, through methods of measuring and quantifying color, and culminates in the practical use of commercially available white light and colored lights. The definitions, metrics, and references discussed will assist in building a critical understanding of the use and application of color in lighting.

It is probably the best, most thorough discussion of light and color available today.  Everyone interested in color, color perception, color rendering, and their relationship to light should read it.  It will be available at the IES booth at Lightfair.

Tags: Color Perception, color rendering, color temperature, CRI, design, LED, LED color, OLED
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LRC Responds to AMA on LEDs

March 27, 2017 in Color, Health, LEDs, Light, Vision

You may remember that in June of last year the American Medical Association (AMA) released a report called “Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting.” The report made some noise in the general press because it supported the idea that blue light from blue-pump white LEDs contribute to disability glare and retinal damage.

In the lighting community there was a considerable amount of frustration and anger over the report for several reasons. First, there were quite a few references cited that were either hearsay, such as a New York Times article about Brooklyn residents who didn’t like their new LED street lights, or were irrelevant, such as several articles about the effect of skyglow on nesting turtles. The other reason was that there was not a single lighting designer or researcher on the panel. Overall, it was a poorly researched paper that didn’t deserve the attention it received.

Shortly after it was issued, the Lighting Research Center at RPI issued a response paper. On March 15 the authors of that paper held a webinar to further address the AMA report. A video of that webinar is now available. If you’ve got an hour, take a look.

The key takeaways regarding the hazard of blue light from LEDs and the report are:

  1. The criteria of blue light hazard for retinal damage is much more than just color temperature, and includes the source size, intensity per unit area on the retina, and SPD of the light source.
  2. Disability glare is not a function of light source SPD, as the AMA paper suggests, although discomfort glare is. Short wavelengths increase discomfort glare.
  3. Color temperature is the wrong measurement to determine whether or not a light source will affect the circadian system and melatonin production because color temperature does not provide complete SPD information.       For example, some 3,000 K LEDs can have a greater impact than 4,000 K LEDs.
  4. The criteria of blue light hazard for circadian disruption from a light source include – the intensity, duration of exposure, timing of exposure, and SPD.

Tags: color temperature, LED color, Light and Health
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Street Lighting and Blue Light Information from the Department of Energy

March 21, 2017 in Color, Health, LEDs

News stories generated by the American Medical Association’s (AMA) community guidance on street lighting has elevated the topic of LED street lighting and its potential effects on health and the environment in the public’s mind. Discussions of these issues have many misperceptions and mischaracterizations of the technical information, and the difference between what has and hasn’t been scientifically established is often blurred.

DOE has assembled a variety of resources on the topic, to provide accurate, in-depth information that clarifies the current state of scientific understanding.

Source: Street Lighting and Blue Light | Department of Energy

Tags: LED, LED color, Light and Health
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How Bright Are Colored LEDs?

January 29, 2017 in Color, Design, LEDs, Light

Measuring and describing the brightness of colored LEDs is an increasingly important part of a lighting designer’s practice. They are used more often, and in more types of projects, than ever before. Yet, we don’t have an accurate method for understanding exactly how much light is being produced and how bright it will appear. It’s a problem that the lighting industry needs to solve, and soon.

The human eye does not respond to all wavelengths of light equally. We have the greatest response to the yellow-green light of 555 nm. Our response falls off considerably in both directions.  That is, wavelengths of light do not contribute equally to our perception of brightness. The sensitivity curve of the human eye is called V(λ) (pronounced vee lambda) and is shown below.

The definition of a lumen, the measurement of brightness of a light source, is weighted using V(λ) and essentially assumes that the light source emits light across the visible spectrum – in other words, it produces a version of white light.

Light meters are calibrated to measure white light using V(λ) so that their measurement of brightness corresponds with our perception. Individual colored LEDs emit only a fraction of the visible spectrum, as shown below in the graph of V(λ) and the SPD of a red LED, and that’s the problem.

V(λ) and the SPD of a red LED.

Light meters measure the light that the colored LEDs provide, of course, and this information is included on an LED fixture manufacturer’s cut sheets, but it often makes no sense. For example, an RGBW fixture I’ve arbitrarily selected reports the following output in lumens: Red 388, Green 1,039, Blue 85, White 1,498. Since brightness is additive, the output when all LEDs are at full should be 3,010 lumens. However the Full RGBW output is given as 2,805 lumens! That’s 7% lower than what we expect.

The essential problem is that the colored LEDs give the light meter only a fraction of the spectrum it’s designed to measure. The meter provides a result based on its programming and calibration, but the results are often nonsensical or at odds with our perception. This problem doesn’t affect only architectural lighting designers. Film and TV directors of photography and lighting directors also rely on a light meter’s accurate measurement of brightness in their work, and when using colored LED fixtures the light meter is likely to be wrong. In fact, even white light LEDs can be difficult to measure accurately because of the blue spike in their SPD.

For now, the only way to accurately assess the brightness of colored LEDs is to see them in use. Lighting professionals need to let manufacturers and others know that the current situation is not acceptable, and that an accurate method of measuring and reporting the brightness of colored LEDs is a high priority. Talk to fixture and lamp sales reps, fixture and lamp manufacturers, and decision makers at IES, CIE, NIST and other research and standards setting organizations. There’s a solution out there. We need to urge those with the skills and resources to find it to get going!

Tags: Color Perception, design, LED color
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About The Author

Jason Livingston IES, LC, LEED Green Associate is the principal of Studio T+L. In addition to his extensive design career, he has taught theatrical and architectural lighting design in New York City since 1993. He currently teaches architectural lighting design at Parsons The New School For Design and Pratt Institute.
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