What it isStructured daily exposure to high-intensity artificial light (typically 10,000 lux for 20-60 minutes), timed to shift the circadian clock. It is the primary non-pharmacological treatment for circadian rhythm disorders.

Why it mattersMorning bright light phase-advances the circadian clock, correcting the phase delay that PTSD’s nocturnal HPA-LC activation produces over time. It requires no prescription and produces measurable PTSD symptom improvement independent of sleep quality effects.

Think of it like thisBright light therapy is like resetting a drifting clock: the light signal gives the circadian system a precise time stamp, correcting the gradual drift that builds up over weeks.

Bright light therapy delivers luminous intensity exceeding the circadian photoreception threshold (~1000 lux) in the blue-enriched white light spectrum (peak ipRGC sensitivity ~480nm), timed relative to the individual’s circadian phase. Morning light (within the subjective day’s first third) produces phase advance; evening light produces phase delay. Standard protocol: 10,000 lux at 30-50 cm distance, 30 minutes, within 30 minutes of waking.

MechanismPhotons activate melanopsin-containing ipRGCs, which project via the retinohypothalamic tract to the SCN. This resets the molecular clock (CLOCK/BMAL1) and modulates melatonin secretion. Morning bright light phase-advances the evening-shifted circadian rhythm, reducing evening HPA-LC activation and improving sleep-onset timing.