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. Author manuscript; available in PMC: 2013 Nov 25.
Published in final edited form as: Clin Geriatr. 2008 Mar 1;16(3):25–31.

Table 3.

Comparison and Contrast between Use of Light for Vision and for Therapy

Parameter Light for Vision Light as Therapy
Intensity needed for effectiveness
  • In task areas: 500 lux

  • In non-task areas (e.g. hallways): 20–30 lux

Varies with spectrum, but typical recommendation is at least 2500 lux of full-spectrum light at the cornea
Duration required for effectiveness Very short (eye registers visual image in less than a second) Longer; varies by light exposure from 5 minutes (for bright sunlight to more than an hour (for typical “light box” therapy)
Wavelength (in nanometers) to which brain is sensitive A broad range (350–750 nm) is needed for vision; peak spectral sensitivity is at mid wavelength (555 nm) 450 – 480 nm (blue light)
Timing of exposure Unimportant Important
Contrast needed for optimal function Spatial contrast is important (differing light/dark patterns at the same time) Temporal contrast is important (contrast in amount of exposure across different times during a 24-hour day)
Evenness of illumination Preferred for optimal vision Not important, though one study showed that light coming from above the horizon (reaching the lower retina) is more effective in suppressing melatonin
Glare Interferes with visual function Interferes with treatment acceptability