• Question from:Paul

I've looked for this on the Internet and I'm sure the answer is out there,but I just don't know where. Whenever I get up before I'm supposed to get up,really early in the morning,it is sometimes light out. If I look at the light then,I can't get back to sleep and get the amount I'm supposed to get. I wear dark glasses for this reason. Also,and it's related, my alarm clock display is red and I have a transformer with a green light. I have two things each shining a different color of light while I sleep,and I always think,"Should I have bought the alarm clock with the blue display?".   

These two situations,the one with dark glasses and the one with the alarm clock, got me thinking about lights and brains. It got me thinking about how seeing light makes people wake up.  I was wondering whether there is a specific wavelength of light that wakes people,or if every light wavelength has a different degree to which it is able to wake people. Maybe they all wake people up to the same degree.How does this light-wake up thing work? I would like to know anything anybody knows about how this works. How does this work? Thank you.

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  • University of Bristol
  • Posts: 4,230

The wavelength of light has a profound effect on our circadian clock. See the google search terms "light wavelength circadian" and specifically:

http://www.science20.com/news_releases/ … ian_rhythm

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  • Milange, Mozambique
  • Posts: 11

You might have been wise to buy the red light alarm clock and not the blue light one. A human's circadian rhythm is synchronised to the external world through light coming from the eyes. There are specific photoreceptors in the eye that are there for this purpose - the photosensitive retinal ganglion cells. These cells are in addition to the rods and cones, which are used for high definition vision. The photosensitive retinal ganglion cells contain a photopigment called melanopsin, often referred to as the circadian photopigment. Melanopsin is most sensitive blue wavelength light, which gives the strongest signal down the optic nerve to the master circadian clock in the brain's suprachiasmatic nucleus. Blue light is therefore the colour of light that most affects the clock and especially in the evening can delay your sleep pattern. For this reason many apps exist for computers and phones (such as f.lux and Night Shift for iOS) which adjust the colour balance of the screen to reduce blue light. There aren't many studies on how effective these apps are, but I find them very useful.