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. Author manuscript; available in PMC: 2010 Jun 1.
Published in final edited form as: Sleep Med Clin. 2009 Jun 1;4(2):285–299. doi: 10.1016/j.jsmc.2009.02.003

Figure 2.

Figure 2

Figure 2 (left). Effect of light on melatonin secretion. Each point represents the mean concentration of melatonin (+/− standard error) for six subjects. Figure 2 (right). Effect of different light intensities on melatonin secretion. The averaged values for two subjects are shown. Symbols: (O) 500 lux; (X) 2500 lux;

(●) 1500 lux; and (□) asleep in the dark. Melatonin levels were measured by mass spectrometry [13]. These early studies were responsible for an increased awareness of the importance of the light/dark cycle as a zeitgeber (time cue) for human circadian rhythms and for the use of the dim light melatonin onset (DLMO) as a circadian phase marker and of bright light as a circadian phase resetting agent in the treatment of circadian phase disorders, including winter depression (SAD) and the circadian disorders experienced by totally blind people. From [21], with permission.