This article raised some interesting discussions in our office. I initially pointed out that yes, higher color temps impact sleep cycles and can lead to S.A.D. But scotpoic vision (low-light visibility) relies much more on the rods in your eyes (which are sensitive to light in the blue-green wavelengths) than it does on the cones (which are sensitive to the reds and yellows). So, from a safety standpoint using a higher color temp is better. There have also been several studies that show increased "perceived brightness" with higher kelvin temps vs. low, so a parking lot lit with a low kelvin source seem darker than the same parking lot with the exact same light levels lit with a higher kelvin source. From a quantitative illumination standpoint, you get more bang for your buck with a higher kelvin temp source used for roadway or parking lot lighting, but from a qualitative standpoint the benefits are more subjective... After all,"One man's glitter is another man's glare." some else then pointed out that Light Adaptation has a much shorter duration than Dark Adaptation such that people are temporarily dark-blinded as they move from a blue-white environment to a dim or dark environment (hence the use of long-wavelength (red) lighting in cockpits and the like to preserve night vision). In a real world application, if a parking lot is lit with high kelvin temp street lights then someone would indeed be temporarily ?dark-blinded? when they leave the lot and pull onto a dimly lit (or ?warmly? lower kelvin temp lit) street. There are pros and cons to high kelvin/cool lighting and lower kelvin/warmer lighting, so it?s an interesting argument.

On one hand, it?s been proven that higher K lighting enhances vision and appears brighter. Therefore it ?feels? safer and less light energy can be used, but at what cost? Higher K lighting more closely mimics daylight so there is definitely a risk of impacting circadian rhythms with continued exposure such as having high K street lights in a neighborhood, and the dark adaptation is definitely a mark on the ?con? side for high K lighting as well.

In the long run I think (or would hope) that lower K lighting would win out since it is generally better for overall human health and more closely mimics the light we see near dawn and dusk. Hopefully there is a way to make it work, but maybe the lawyers will win by arguing the public safety/security aspects of higher K lighting.