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 |
|
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 |