Photoresponses

Photoresponses refer to observable reactions to light exposure across biological and physical systems. In biology, they include processes such as photosynthesis, phototropism, circadian entrainment, photoperiodic control of flowering, and pupil reflexes. Plants use photoreceptors—phytochromes, cryptochromes, and phototropins—to detect red, far-red, blue, and other wavelengths, translating light cues into changes in growth, metabolism, and development. Circadian and seasonal responses synchronize with the day-night cycle and photoperiod. In animals, light influences behavior and physiology through retinal and non-visual photoreceptors, affecting sleep, hormone release, and reflexive responses such as pupil constriction.

In the physics and engineering sense, photoresponse describes the current or voltage generated by a photosensitive device in response to light. Photodiodes, phototransistors, CCD/CMOS sensors, and solar cells exhibit photoresponses characterized by responsivity, spectral sensitivity, rise and fall times, linearity, and noise. Quantum efficiency describes how effectively absorbed photons are converted into charge carriers.

Photoresponse measurements are central to vision science, plant biology, and optoelectronics, and advances in photoresponsive technologies underpin imaging, communications, and solar energy. The term encompasses a broad set of light-induced phenomena, from cellular signaling and plant development to the performance of detectors and energy conversion devices.