IES Disagrees With AMA on Night Time Outdoor Lighting

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.

A New Report on LED Color Shift

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.

How Bright Are Colored LEDs?

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!

IES Symposium Summary

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.

  • TM-30-15 is seeing broader acceptance throughout the industry. In an exciting development, it seems that the CIE is going to endorse TM-30 Rf after a few changes are made. The expectation is that the industry will then begin a rapid movement toward using Rf instead of CRI Ra, and that eventually CRI will be withdrawn. Unfortunately, the CIE is notoriously slow, so there is no timeline for their formal endorsement of TM-30. Maybe next year?
  • Manufacturers are resolving the spectral deficiencies that result from using a limited number of LEDs in both color mixing and color temperature tuning products. Their solution is to move from two and three color systems to systems using four or five independently controlled colors of LEDs.
  • Color preference was a big topic with no resolution. One complaint of both CRI and TM-30 is that they penalize light sources that deviate from the reference source even if many people prefer the deviation. Of course, Ra and Rf are both fidelity metrics, so they must penalize such deviations.   We have strong evidence that people prefer light sources that slightly increase the saturation of objects, and that people prefer light sources that include somewhat more red than the reference sources. However, because the amount of deviation that is preferred is application dependent, a single, all-purpose metric for rating color preference seems to be unattainable.