We know that melanopsin is sensitive to blue light with a peak around 480 nm and that melatonin suppression is most sensitive to blue light with a peak around 460 nm. Furthermore, it seems that melanopsin is important but not essential to circadian photoentrainment. I have found some older reports showing that circadian phase shifts are more sensitive to short wavelength light.
Does anyone have any idea of how important blue light is to circadian photoentrainment, preferably based on recent research?
One of explanation should be that the blue light has more energy as compared with red light
Taking into consderation that E=hv, will get 460 nm (blue): 750 nm (red) =0.61, thus energy of blue light 1.6 times more than that of red one.
Lots of experimental evidence are available to support that monochromatic light shift the clock, especially blue light compared to red light. Blue light shifts the clock (circadian locomotor activity rhythm) but not red light. When we keep animals in constant DD, people have been using constant red light. if you keep the animal in DD, blue light exposure definitely shifts the clock.
From an EEG perspective blue EMG correlates, i.e., high amplitude low frequency brain waves are associated with greater long distance connectivity in the brain.
The recent consensus report is Trends Neurosci. 2014 Jan;37(1):1-9. doi: 10.1016/j.tins.2013.10.004. Measuring and using light in the melanopsin age.
As Chidambaram Ramanathan says, if you want humans to entrain to light the stimulus must include mid-short wavelength light (green-blue-violet). Probably.
There are many publications that support the idea that blue light is most effective in influencing circadian rhythms:
http://www.nature.com/nrn/journal/v15/n7/full/nrn3743.html
http://www.ncbi.nlm.nih.gov/pubmed/25726691
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