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  This is especially true when the science is out of date and produces results that don’t necessarily agree with our vision and/or perception.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.

LRC Responds to AMA on LEDs

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.

Light and Color Perception

NPR’s All Things Considered had a brief piece about light and color on Monday. The main thrust of the story was that color is not inherent in an object, but is perceived and interpreted by our brain, but there’s much more to revealing and perceiving the color of objects. Here’s a quick overview.

To begin, all objects have light reflecting properties. Objects that we identify as red reflect most of the red light that falls on them and absorb the other colors. Likewise for objects that appear to be green, blue, etc. Objects that appear to be white reflect the colors of light more or less equally, while objects that appear to be black absorb most of the light that falls on them. Objects only reflect light, they don’t create it, so if we use blue light to illuminate an object that reflects red light we find that no light is reflected and the object appears to be black.

As I explain in Chapter 8, we change the balance of the colors in white light every time we change the light source. Even with a single light technology, such as fluorescent, we change the balance of colors when we change from cool white to warm white. The color content of a light source can be measured (it’s called the spectral power distribution or SPD) and graphed as shown below.

SPD of Daylight
SPD of Daylight

 

SPD of a Cool White Fluorescent
SPD of a Cool White Fluorescent

When we change the SPD we change the colors of light that are available for reflection by objects, which means that we also change the balance of light that is reflected and thus the color information that our eyes receive. The result is that changing the light may change the color appearance, or the apparent color, of an object. Many of us have had the experience of buying clothing or paint that was one color in the store and another color at home. Here we see this phenomenon with a color/materials board illuminated by several light sources.  How well a light source enables us to perceive colors is called color rendering.

Illuminated with Incandescent Lamp
Illuminated with Incandescent Lamp
Illuminated with Warm White Fluorescent Lamp
Illuminated with Warm White Fluorescent Lamp
Illuminated with Cool White Fluorescent Lamp
Illuminated with Cool White Fluorescent Lamp

Color and brightness perception are both relative not absolute. A candle in an otherwise dark room may seem too bright to look at directly, while its brightness on a sunny day seems insignificant. In addition to the effect of SPD on our color perception, colors are perceived in relation to one another, especially between foreground and background as shown below.

The color of the dots is the same in both figures.  The strong background colors affect perception of foreground colors.
The color of the dots is the same in both figures. The strong background colors affect perception of foreground colors.

If I can demonstrate shifting our color perception why don’t we experience it in everyday life? Why are my blue jeans blue and my red car red in nearly every lighting situation? The answer is color constancy or chromatic adaptation. It does us no good to spend time and energy struggling to figure out colors. We want to be able to tell if a piece of fruit is ripe regardless of the lighting conditions. Color constancy is our brain’s use of information gathered from the entire visual field to understand the lighting conditions and calibrate our color perception so that color shifts are minimized.

“Design Guidelines for the Visual Environment” Comment Period

The Low Vision Design Committee of the New Buildings Institute has release a draft of its new “Design Guidelines for the Visual Environment” for public review and comment.  The intent of the guidelines is to offer assistance to design professionals and others in accommodating those  with a variety of vision disorders.  Click here to visit the NBI site to download the draft.