Light

Light is visible electromagnetic radiation that stimulates photoreceptors and enables vision. Its daily and seasonal patterns also provide organisms with a major environmental timing cue.

Phototransduction: The process by which photoreceptor cells convert absorbed photons into electrical signals. It is the first step by which light becomes a neural signal.
Electromagnetic spectrum: The complete range of electromagnetic radiation, ordered by frequency or wavelength. Visible light occupies only a narrow band of this broader spectrum.
Photoperiodism: The biological response of organisms to the relative lengths of day and night. Light duration cues seasonal flowering, reproduction, and other life-cycle changes.
Infrared: Electromagnetic radiation with wavelengths longer than visible light and shorter than microwaves. It can affect biological systems but lies beyond ordinary human vision.
Photoreceptor: A sensory cell or molecule that detects light and initiates a biological response. Photoreceptors are the cells that capture light for vision and timing.
Visible spectrum: The range of electromagnetic wavelengths detectable by typical human vision. It defines the portion of radiation called visible light.
Light therapy: The use of controlled light exposure to treat or manage health conditions. Timed bright light can shift circadian rhythms and treat seasonal affective disorder.
Ultraviolet: Electromagnetic radiation with wavelengths shorter than visible light and longer than X-rays. It is adjacent to visible light but is generally not seen by humans.
Melanopsin: A light-sensitive photopigment found in retinal ganglion cells and several other tissues. Melanopsin helps relay ambient light levels to the body's clock.
Photon: The quantum of electromagnetic radiation, carrying energy proportional to its frequency. Photoreceptors respond to light by absorbing individual photons.

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