Intensity needed for
effectiveness |
|
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 |