Friday, November 11, 2016

Shining light onto LEDs - disturbing findings

Fly into any major city at night and you’ll notice vast swaths of bright white lights replacing the yellow hue from high-pressure sodiums, once the preeminent lord of night lighting across the urban fabric.

The white light is from LEDs - light emitting diodes - and cities are installing them in an implementation tsunami. They are cheaper and they are brighter, but I have been bothered by their excessive glare and, during our night site visits, I always warn students about the lack of research on LED and human behavior. Over the years I’ve blogged about sodiums and Randy Atlas has guest blogged here on LEDs. But research has been scant.

Until now! And the early results are worrying.


The American Medical Association has released a statement condemning the health effects of LED street lighting.

The AMA identifies two concerns:

  • First, the bright glare is caused from the wavelength and color rendition from LEDs. Apparently the high intensity of LEDs emit large amounts of blue light that appears white. This causes a glare problem worse than conventional street lights and it’s why the light dispersion from LEDs is so difficult to control, even with cutoff shields. Says the AMA: “Discomfort and disability from intense, blue-rich LED lighting can decrease visual acuity and safety…creating a road hazard.”

Engineers use a color rendition index to assess light sources impacts 
- photo by Adoniscik 

  • Second, it also turns out that the blue-rich LED streetlights suppress melatonin levels and people end up with disturbed sleep cycles. Says the AMA: “It is estimated that white LED lamps have five times greater impact on circadian sleep rhythms than conventional street lamps.” In large studies the AMA says this causes “reduced sleep times and impaired daytime functioning”. Not good.

Obviously, the AMA studies are not the final word. For example, the blue from LEDs can be controlled.


The lighting industry, understandably, is not happy with the AMA conclusions. One source says “As with any new technology, there are a lot of unknowns that only time will be able to tell what the results/answers will be.”

That is the same thing we have been saying about LED lights from the beginning. In the budget-saving rush to install LEDs we know very little about the behavioral, social and medical consequences from these new light technologies.

Students of CPTED know that lighting research regarding safety is based on quantity, not quality. I have yet to read a single study on light source quality and crime related behavior. This knowledge gap isn't limited to LEDs, we also have inadequate qualitative information on halide or sodium light sources.

Until we do, it’s probably best to look for successful cities with exceptional lighting, such as Melbourne, Australia, and see what they do right.

Melbourne, Australia has award-winning, city-wide lighting designs - photo by
the extraordinary lighting engineer Ian Dryden