How it works  Intensity
  Medical research shows that relatively low brightness (as low as 100 lux, like a very dark day) is enough to cause alertness and shift of Circadian Rhythm.  Light of any wavelength decreases the secretion of Melatonin.  Melanopsin at the eye retina detects the light level and sends signals to the Pineal Gland.  When it starts to get dark, the Pineal Gland synthesizes and secretes Melatonin.  
     
   
   
  The graph1 shows the light intensity of 300 lux suppresses the body to secrete 40% less Melatonin than 100 lux.  Thus, in the few hours leading up to bed, the light level in the room should be dimmed down substantially, so that the brain can register that it is getting dark now.  
   
 
 
  1 Duffy, J.F. and Czeisler, C.A. (2005) Effect of Light on Human Circadian Physiology, Sleep Med Clin. 2009 June; 4(2): 165-177  
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