The sun has always held a prominent place in society. It has been worshipped as a god for its life-giving rays, as well as by those who have desired deep bronze tans on the beach. More recently, sunshine has been recognized for its importance in helping the body manufacture vitamin D, and it has been studied for its potential impact on mood, specifically, on depression. Moderating the hours of sunlight (or the equivalent of brightness) may have an impact on sleep cycle, and those using bright light therapy (BLT) to improve sleep may find improvements in mood.


Background


BLT, sometimes known as phototherapy or heliotherapy, is used in multiple ways and for a variety of conditions. Newborns with jaundice are routinely treated with light therapy, often referred to as a bili light,1 and BLT is used extensively in dermatology for conditions such as psoriasis and acne.2 Whereas these applications of BLT have been accepted practice for decades, the impact of BLT on mood disorders is less studied and not well-documented by appropriate clinical trials. 


Science 


The mechanism of action of BLT is thought to be multifaceted. As light contacts the retina, a variety of actions are set in motion. Two key processes are the suppression of melatonin and the activation of serotonergic systems.3

The earliest use of BLT was for seasonal affective disorder (SAD). Commonly called holiday depression, SAD is linked to the natural decrease in sunlight during the winter season.4 In a study by Reeves et al., participants diagnosed with SAD were randomly assigned to therapy with either low-intensity light (placebo) for 1 hour or BLT for 1 hour.4 Results showed significantly improved Beck Depression Inventory II (BDI II) scores in the BLT group compared with the placebo group. 


BLT has also been considered for nonseasonal depression. In one small study, researchers randomly assigned 15 patients with confirmed depression, impaired circadian rhythm, and poor sleep quality to either BLT alone or BLT in combination with fluoxetine.5 Both groups were treated with 30 minutes daily of 10,000 lux BLT, and one group also continued taking daily fluoxetine. At the end of 7 days, BDI II and Hamilton Depression Rating Scale (HAM-D) scores showed no statistically significant difference between the two groups. Although this may be an unimpressive result, it does confirm that BLT is at least as effective as fluoxetine for this condition.5