I've worked on a few street light retrofit projects and the AMA warning is a little overblown and frankly immediately outdated. This is off the cuff, but it co

I've worked on a few street light retrofit projects and the AMA warning is a little overblown and frankly immediately outdated. This is off the cuff, but it comes down to circadian rhythms being influenced by the color of light. Before artficial light, the sunrise and sunset have a softer light with a lot more red wavelength in it. This would correspond more closely with the color of light from an incandescent, like 2500-3000 Kelvin. The mid day light has a lot more blue wavelength in it relatively, where it is much more of a White light, I think daylight is like 15,000K. The high pressure sodium, HPS, lights have an orange light in the 2,200K range. The majority of LED street lights being installed are 4000-5000K, so they have a lot more of the blue light. Essentially the blue light tricks your brain into thinking it's mid day and messes with your sleep patterns. The first generations of LED street lights could really only effectively make the 4000-5000K light. With new generations coming out every 3 months or so though they have been able to create models that can generate the 2500-3000K warm red light, but they're not quite as energy efficienct as the 4000K lamps, maybe 10% or something. The 2500K is actually better for the Dark Sky movements as well and a lot of cities are moving to specify these warmer temperature for those reasons. There are a whole bunch of other things going on as well. The road way lighting standards were designed around the light patterns of a HPS lamp and haven't been updated to reflect the light patterns possible with LEDs, hence a lot of LED projects have too bright of streets. For the sleep pattern issues, when you're installing LED lights in your home, you want to put the warm lamps, 2500-3000K, lamps in bedrooms and such. Then for living spaces or offices you'd want to put the 4000K lamps to help keep you awake during the day. There are also lamps/fixtures available that will automatically tune the color output of the light to be in sync with the outdoors to help keep circadian rhythms in sync. This company has been pushing the tunable lamps hard. http://www.planled.com/archives/portfolio-item/entraining-circadian-rhythms http://www.planled.com/archives/portfolio-item/entraining-ci... http://humancentriclighting.org/ http://humancentriclighting.org/ This site appears to be fairly dead, but they were more of an independent group promoting it the last year or two.