What's the difference between full-spectrum bulbs and light therapy lamps for sad?

Name only, usually.: Full spectrum bulbs should have the same mix of light rays that sunlight does or they are not full spectrum bulbs. To be effective light therapy lamps should also try, as much as possible, to mimic the suns' rays. It is easier to do so with larger lamps. Some portable led lamps will not usually have that advantage.

Visual spectrum: There are receptors in the back of the eye that are thought to play a role in using light to treat seasonal affective disorder. These receptors respond to light waves within the visual spectrum. A full visual spectrum bulb is fine, however you do not want a truly full spectrum bulb as you do not want to expose your eyes to the infrared (heat) or ultraviolet (cell damage) rays.