(A) BLT corrects the phase delay. Pre- and post-BLT treatment are displayed as blue and purple broken lines respectively. Morning BLT treatment corrects the phase delay by shifting the circadian rhythm earlier (to the left) leading to less discordance between the circadian rhythm and the clock time/sleep-wake cycle.
(B) BLT increases available serotonin. BLT treatment during the fall/winter reduces the serotonin transporter binding potential, theoretically leading to less uptake, and a greater amount of available serotonin in the synaptic cleft.