CIRCADIAN Lights

The first “eye-opening” discovery was that blue light - the color of the cloudless sky – regulates the timing of our biological (“circadian”) clocks. While natural daylight, or artificial white light, is comprised of rainbow color mix of multiple wavelengths, it is predominantly the blue wavelengths that keep our circadian rhythms and sleep-wake cycle in synch with the rising and setting of the sun. By shining lights with monochromatic single colors into people’s eyes the unique sensitivity of circadian rhythms such as melatonin to blue wavelengths was discovered.

This blue wavelength sensitivity cannot be explained by the spectral sensitivity of the rods and cones in our eyes. For over a hundred years we have known that daytime color vision relies on cone receptors that provide color information to the brain. While the cones can respond to all colors in the visual spectrum, they are most sensitive to green light. Nighttime vision is dependent on rod receptors that can see even when light levels are very low. The pathways that carry visual images from the rods and cones to the brain have been well mapped and understood. But neither rods or cones are highly sensitive to the blue wavelengths that reset circadian rhythms and suppress melatonin.

The second key discovery, which explained the blue light sensitivity, was the identification of special type of photoreceptor cells in the retina containing melanopsin, a photo pigment with a peak sensitivity to 460nm blue light. The melanopsin receptors are 25 times more responsive to light at this blue wavelength than to full spectrum white light. When activated by blue light, the melanopsin receptors send information via a special nervous pathway directly to the suprachiasmatic nucleus (SCN) in the brain, quite separate from those that carry visual images to the brain. The SCN is the body’s “master circadian biological clock”. It thus became clear that, just like our ears have the two functions of hearing and balance, our eyes have the two functions of seeing visual images and regulating the brain’s master circadian clock. 

The third key invention, the Gallium Nitride based LED, came out of semiconductor industry in Japan and has revolutionized the world of lighting, with the inventors winning the 2014 Nobel Prize in Physics. The invention of LED light sources was a huge breakthrough in terms of the efficient conversion of electric power into light. Today’s highly efficient LED lighting systems provide over 100 lumens per watt compared to only 10-15 lumens per watt from incandescent light bulbs. But this efficiency is achieved by using Gallium Nitride (GaN) LED chips which primarily pump out blue light in the 440-470nm range. The LED dies are coated with phosphor materials to convert the GaN emitted blue light into a broader spectrum white light. The selection of the 440-470nm blue range is largely driven by lumens per watt and production cost efficiency.

The problem is that the 440-470nm blue light emission spike of these widely sold blue-pump LEDs causes maximum stimulation of the melanopsin retinal ganglion cell receptors and the non-visual pathways controlling the circadian timing system and pineal. Because of these spectral characteristics these conventional blue-pump LEDs are much more potent suppressors of pineal melatonin with its attendant disruptive health effects. With LED lighting projected to replace over 50% of the workplace lighting by 2020 we have an impending catastrophic collision between technological advance and human health and well-being.