Ambient Light

Ambient light sensors use photodiodes or phototransistors with spectral response curves designed to approximate human eye sensitivity (photopic response), measuring light intensity in lux units. When photons strike the semiconductor material, they generate electron-hole pairs proportional to light intensity, producing a measurable current. Advanced sensors include filters to measure specific wavelength ranges relevant to circadian biology—particularly blue light (460-490nm) which suppresses melatonin production. In wearables, ALS enables automatic display brightness adjustment to improve battery life and user comfort, helps filter optical sensor artifacts by detecting environmental light interference, supports circadian rhythm tracking by monitoring daily light exposure patterns, and assists wear detection by distinguishing covered (worn) versus exposed (removed) states.