My NP recommended one for me and so I bought it. It is a "full spectrum" light bulb and it replaces a regular bulb in my lamp.
It simulates the light emitted from the sun.
I don't find any change for me, but then again, I don't use it every single day.
Here is something I found about how it is supposed to work: The therapeutic level of illumination has several known physiological effects, though its mechanism of effect is still unclear. Blood levels of the hormone melatonin, which may be abnormally high at certain times of day, are rapidly reduced by light exposure. Depending on when bright light is presented, the body’s internal clock - which controls daily rhythms of body temperature, hormone secretions, and sleep patterns - shifts ahead or is delayed when stimulated by light. These physiological time shifts may be the basis of the therapeutic response. On the other hand, the antidepressant effect may not involve rhythm shifts, but rather overall changes in neurotransmitter (chemicals involved in the communication between brain cells) activity. Neurotransmitters such as serotonin and dopamine may be prime candidates. Research into possible mechanisms is currently underway, and the final answer is not yet in.