Hey, Thanks for bringing this topic up. Can someone please help me with a question that I have? If a LED light is rated at say 5000K is that the true Kelvin or the perceived Kelvin? In other words, is it actually emitting a higher Kelvin than advertised but we are unable to consciously detect? Thank you,

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.

Thanks for the info.,Mike. As I read these comments I am forced to go back to what I thought I knew about light. Is not light the result of a frequency? Is this frequency related to time of day? Is not light from the sun at noon at a level that exceeds the 6000K level? Do these studies suggest that it is dangerous to be working in mid day outdoor conditions? When I was working in school maintenance I was advised to use "daylight" bulbs in the classroom because they provided a more blue light, hence a more full spectrum light that made visibility greater with lower lumens. Could our perceived problem be more a result of intensity rather than color rendition? Do we just need better blinds in our bedrooms? Anyway, more questions than answers!

I admit I did not read the inserted links. It was not because of doubt or disinterest. I have read scores of papers on this subject for over 50 years. It is a well established fact that light frequencies usually expressed as Kelvin, the higher the Kelvin the higher the frequency or on the EMf scale the closer the movement toward blue, can affect health. The problem is general. When LEDS first entered the mass market they were described as cool light and the engineers treated them as such by failing to engineer appropriate heat sinks. Thereby the LEDs failed after short use though their normal life should be very long. Engineers are not very good at quantum theory something that must be studied to understand the deeper physics of electricity and light. By the way it is more than a joke when scientists say that if you think you understand quantum theory that is proof you do not understand it.

Wow. So, drivers can now see too clearly, they can distinguish colors too well, they have too high visual acuity compared to the old yellow candles, and - gasp! - they might be temporarily inhibited from secreting a hormone that puts you to sleep!

Horror of horrors...we may accidentally have saved countless lives by installing 4100k or even 5000k LED streetlights due to driver's inability to fall asleep...while driving down the highway!

What a load of bull, all the way around, as far as the majority of public area and street installations. I only hope that my tax money wasn't wasted on these ridiculous studies.

On the other hand, I totally sympathize with those in a sleepy residential neighborhood who may have a one-light-fits-all streets dept who may incorrectly put a massive output LED meant for the highway - possibly with no optics and no cutoff - next to their home. They may suddenly have a 5000k spotlight shining into their bedroom. Appropriate selection of quality light engines, filtered for UV (as ALL of the spec-grade ones are, to eliminate harmful UV output), and intended for the application, is important. That avoids any adverse health effects, wellbeing issues, or whining.

No doubt invisible light can alter your health in as many ways.

Can the same color argument be made about the older Mercury Vapor lamps or Metal Halide? Metal Halide are a very bright white light and you could see the blue tint of many of the mercury vapor ones. Or is it just a brightness issue? When High Pressure Sodium came out we had police telling us they gave a better color rendition.

Many, if not all, cities are using the low light pollution designs in whichever type lamp is used.

The health effects of light at night is a real problem in the US. Thank you for posting this article Mike Holt