Fig. 3.

Exposure to room light before bedtime decreases melatonin (MLT) levels. A, Histogram showing the percent decrease in melatonin from melatonin onset to bedtime when participants were exposed to room light (<200 lux) vs. dim light (<3 lux) until scheduled sleep. The AUC of the melatonin profile was determined in dim light and compared with the AUC on the preceding day at the same relative clock times. Median percent decrease in melatonin is indicated by the vertical line with label. B, The melatonin rhythm is shown for three representative volunteers exposed to room light (○) before and after scheduled sleep in darkness (enclosed by the vertical dashed lines) vs. exposure to dim light (●) at the same relative clock times on the following day.