A reader asks:

 I would like to know if there is a difference between a UV blocked full-spectrum and a broad-spectrum light box.


The terms “full spectrum” and “broad spectrum” are not precise technical terms. Full spectrum–which is really just an advertising term–was developed as a type of broad spectrum lamp that emphasized short-wavelength emission, including UV. “UV-blocked full spectrum” is therefore a contradiction in terms. Furthermore, UV-blocking is incomplete using cheap plastic diffuser screens, leaving the opportunity for skin reddening and puffiness (even burning) in people with sensitive skin. These lamps may also cause retinal photosensitization when used in combination with various drugs.

Broad spectrum lamps include all fluorescent lamps with a white or whitish appearance. They are differentiated by “color temperature”, as measured in Kelvins. Full spectrum lamps have very high color temperatures (5500 Kelvin and above), which cause considerable visual glare at the high intensities used therapeutically. They are also electrically inefficient and more expensive than alternatives. Broad spectrum lamps of 3000-4000 Kelvin are much easier on the eyes and are equally effective therapeutically. We specifically recommend 4000 Kelvin lamps with complete UV filtering, based on the most recent clinical tests at Columbia University. For people whose doctors have recommended reduced blue exposure, to allay age-related macular degeneration, we recommend 3000 Kelvin lamps.