Designing With Light is available in English as a soft back book and as an ebook for Kindle, Nook, iBooks, and the Google Play Books app. It is also available in Simplified Chinese as a hard back book.
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June 22, 2020 in Psychology, Vision
A fascinating article from Vox.com about perception. The science of optical illusions shows that “reality” is constructed by your brain.
Source: How do you know what you see is “real”?
September 16, 2019 in Color, Design, LEDs
Last Thursday Donald Trump spoke to a group of Republicans in Baltimore. One of the things he said caught my attention: “The lightbulb. People said what’s with the lightbulb? I said, here’s the story. And I looked at it, the bulb that we’re being forced to use, No. 1, to me, most importantly, the light’s no good. I always look orange. And so do you. The light is the worst.”
Now, I’m not aware of being made to look orange under LEDs, nor have I ever noticed LEDs making my friends, colleagues, or students appear orange. You can’t imagine how embarrassed I’d be if it turned out that a real estate developer and entertainer had more astute color perception than me, a lighting designer and Co-Chair of the IES Color Committee. If our only means of evaluating the color rendering of a light source, and evaluating the orange content specifically, was CRI we would have no objective way of testing his statement. CRI, technically Ra, is a single value that gives us an average of the match between the light source in question and its reference source (either a blackbody radiator or a CIE definition of daylight, depending on CCT) using only eight color samples.
Since Ra is an average value there’s no way to understand the rendering of any particular hue. I’ve talked about this here. However, one of the wonderful things about ANSI/IES TM-30 IES Method for Evaluating Light Source Color Rendition is that we can use it to test that claim. TM-30 uses 99 color samples that are distributed across the color space and the visible spectrum.
It also breaks the color space up onto 16 Hue Bins, each one covering a specific range of the color space. In the case of orange, we want to look at Hue Bin 3. Specially, we want to look at Rcs,h3 (the subscript CS stands for Chroma Shift) which quantifies the increase or decrease in the saturation or vividness of orange compared to the reference light source.
So, let’s put the science of TM-30 to work and see if we really do know that LEDs make us look orange!
The TM-30 calculator contains a library of 300 SPDs (spectral power distributions), of which 137 are commercially available white LEDs. The CCTs range from 2776 K to 6123 K. If white light LEDs really did make us look orange we’d expect to see a large majority of them have a positive Rcs,h3, probably with an average chroma shift in excess of 10%. In fact, the 137 SPDs have Rcs,h3 that range from -8% to 1% with an average of -3.6%, a decrease (not an increase) in the saturation of orange. It’s not me, it’s him. TM-30, which uses the most modern models of human vision and a set of colors that cover the color space and visible light spectrum, proves it. What a relief!
Don’t believe me? Download TM-30 and the calculator for free from the IES web site and see for yourself.
Of course, I’m not saying LEDs are perfect light sources. Like any other product there are good ones and bad ones. However, TM-30’s measurements of fidelity and gamut (as averages) and measurements of fidelity, chroma shift, and hue shift (by hue bin) permit us to make a thorough evaluation of a light source to understand its color rendering characteristics. Using this knowledge, we can determine if a particular light source distorts colors and is appropriate for a project, or not.
I should take a moment to note another error he made when he said, “And very importantly—I don’t know if you know this—they have warnings. If it breaks, it’s considered a hazardous waste site. It’s gases inside.” Perhaps you’ve heard the acronym SSL or the phrase solid state lighting. LEDs are a version of SSL, which means that they are…well, solid. Unlike previous light producing technologies LEDs are a solid combination of materials. As such, if one were to physically break (which is unlikely since LEDs are small, are mounted to a heat sink and often covered with a lens, so you’d have to break a lot of materials simultaneously) no gas, hazardous or benign, is emitted. He’s thinking of fluorescent lamps and the small amount of mercury they contain. Even then, a broken fluorescent lamp doesn’t turn the area into a” hazardous waste site.” Here are the EPA’s instructions for cleaning up a broken fluorescent lamp.
April 2, 2018 in Color, Education, Lighting Profession
On April 19th Wendy Luedtke (my co-chair of the IES Color Committee) and I will be presenting a free IES webinar called Design for Color and Illumination. Here’s the blurb from the IES site:
When developing a lighting design, lighting specifiers determine the lamp and fixture combination that best suits the design’s requirements based on many factors. While some considerations are largely technical, such as power consumption, the amount of light generated, and how light is distributed, one consideration is both technical and artistic and can be approached in a number of ways. Participants to this webinar are eligible for one (1) IES Continuing Education Unit (CEU).
The webinar is at 12 noon EDT. Register here.
November 17, 2017 in Color, Design, Light, Luminaires
Today Focal Point Lights of Chicago, IL introduced a series of fixtures that feature what they call Preferred Light. Preferred Light is based on recent studies at PNNL and Penn State, plus their own study, and uses TM-30’s Rf, Rg, and Hue Bin 16 values to establish a balance of fidelity, saturation, and red rendering that is “visually appealing to humans.”
The overall idea is that people seem to prefer a light source that slightly over saturated most colors, especially red. “Using a custom LED mix, Focal Point defines Preferred Light using TM-30-15 metrics as having a fidelity (Rf) of 89, a gamut (Rg) of 107, and over-saturating Hue Bin 16, deep red content, by 9% at a [Correlated] Color Temperature of 3500K.” So, by using the statistical measures of TM-30 and applying them to the related topic of color preference Focal Point has identified an optimized set of LED products to meet their customers’ needs.
I’ll be the first to admit that it may be risky to base all of this on only three studies, but other studies have shown that the TM-30 results can be applied in this way, and are also showing us the relative importance of the various calculated values. I’m excited to see the industry using the tools, and am looking forward to seeing the Preferred Light for myself.
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.
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.
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.
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!
April 6, 2016 in Color, Design, Light
If you missed IES Research Symposium III Light + Color you missed an exciting (for color geeks) few days. It would take too long to relate everything that was discussed, but here are some key highlights.
January 28, 2016 in Color, Design, Education, LEDs, Light, Lighting Profession
A few weeks ago I gave a three-hour seminar on lighting museums and galleries to the graduate students in an art curating program at a university here in New York. Condensing everything I’d like to say into less than three hours was tough. The two big questions were what to include and what to leave out. I started with a quick overview of how to think about light and lighting before moving on to basic vocabulary and some common lighting techniques. Then, since LEDs are clearly the future, even when lighting art, I moved on to an overview of both color temperature and color rendering. I talked about reference materials such as the IES Lighting Handbook, intensity and brightness ratios, and other considerations before we moved into their gallery space to use their track light system for some demonstrations.
After the whole affair a faculty member, who sat in on most of the seminar, said he had hoped I would have spent much more time talking about how to use track lights and less time on unimportant issues like design, color temperature, and color rendering (!). I was respectful, but stunned. Focusing track lights is so complex that it requires extensive demonstrations? Understanding that with LEDs the color qualities of the light vary widely, and can only be properly selected when they are understood is unimportant information? Uhh…NO. Or, as my 20 month old niece says, “no no no no.”
Yes, five or ten years ago the default light source in museums was an incandescent or halogen lamp. The color temperature difference was minor and the color rendering of both was excellent. That’s not true today. Look at the cut sheet for any museum grade track light and you’ll see that you have a choice of several color temperatures and CRI values. If ANYONE needs to understand the qualities of light that must be selected when using LED fixtures, if anyone needs to understand the affect that color temperature and CRI have on how colors are perceived, it’s certainly people involved in displaying and lighting art. To me, that means the curators of exhibits and the lighting designers they hire.
As I’ve discussed earlier, changing the color temperature of the light changes the color appearance of objects, as shown below.
Illuminated with 3000 K light
Illuminated with 4000 K light
The phenomenon of color consistency means that the shift in color appearance isn’t as great as one might expect or as these photos suggest, but the shifts are real. If you’ve ever bought a black garment only to discover later that it was actually dark blue you’ve experienced this shift. A similar thing happens when we compare a high CRI light source and a low CRI light source. If your work involves color perception this is basic and critical information.
Curators can be forgiven for not knowing much about this, but if they know nothing how can they collaborate with their lighting designer to show the art as they intend? Administrators and curators of museums and galleries – educate yourselves, then hire a lighting designer!
