I thought there are only cones and rods in the eye to make us see but we also have something called a “third” class of ocular photoreceptors, photosensitive retinal ganglion cells (pRGC), different from the rods and cones within the eye.
Based on light intensity and wavelengths or colors, these specialized neurons regulate a wide range of physiology and behavior:
They plays a major role in synchronizing our rhythms to the 24-hour light/dark cycle, providing primarily length of day and night information by sending light information directly to our brain to synchronize our rhythm or our internal clock. They further regulate the pupil size and other behavioral responses to ambient light conditions
And regulate the release and suppression of melatonin which helps to let us fall asleep or wake up
We need light in the morning and then darkness in the evening to set our circadian clocks. Kids go straight to school after waking at times so early that much of the year it is still dark. They don’t see natural sun light until late in the day, if they do at all. A well-lit class room is illuminated at about 400 lux; compare that to the 10,000 lux experienced outdoors on a dull, rainy day or the than 100,000 lux experienced on a bright day. Is it any wonder they don’t know when to go to sleep?
That wavelength of 480 nanometers which the retinal ganglia are sosensitive to, is in the blue spectrum, in fact, it is pretty much the color of the sky on a bright sunny day. This knowledge has triggered some interesting attempts to reset circadian rhythms.
Mariana Figueiro at the Lighting Research Center at Rensselaer Polytechnic Institute in New York, proposed using orange-tinted glasses and light boxes as therapy for tired teens a few years back. Her idea was to expose the kids to the right kind of light at the right time of day to bring their sleep cycles back in line. Orange glasses are used in the evening can filter out blue light and prevent melatonin suppression. Light boxes with blue LEDs used in the morning can suppress melatonin and wake the kids up. Apparently she did not get adequate funding to adequately test this idea and her work has not been published yet.
For some more background read this article of Jacob Schor
Or listen to the “webseminar”: http://www.lighting.philips.com/main/connect/Lighting_University/upcoming-webinar.wpd presented by professor Serge Daan
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