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Photonic Zeitgeber Effect

Meaning

The Photonic Zeitgeber Effect describes the profound, phase-shifting influence of light exposure, particularly bright, short-wavelength visible light, on the human body’s master circadian pacemaker, the suprachiasmatic nucleus (SCN). As the most powerful external time-giver (zeitgeber), light acts as a non-pharmacological signal to entrain, or synchronize, the endogenous 24-hour biological rhythm with the external day-night cycle. This effect is crucial for regulating the timing of sleep, alertness, and rhythmic hormone secretion.