What effect does exposure to bright light before subjective night have on the circadian clock?

Exposure to bright light before the subjective night generally causes a delay in the circadian clock. The circadian rhythm is influenced by external light cues, which are processed by specialized cells in the retina that relay information about light levels to the suprachiasmatic nucleus (SCN) in the brain. When bright light is introduced in the hours leading up to what an individual perceives as night, the SCN may adjust the timing of the circadian rhythm, pushing it forward to a later time. This effect is a part of the complex interactions that help align our internal biological clock with the external environment, making light an essential regulator of circadian timing.

While bright light can surely suppress melatonin production, which typically occurs in the evening as darkness approaches, the primary effect regarding the timing of the circadian rhythm is its delay when exposure occurs before the subjective night. Therefore, recognizing that bright light is a potent zeitgeber (time cue) is crucial for understanding its impact on circadian biology.