Redlight

Red light, or redlight, denotes the portion of the visible spectrum characterized by wavelengths around 620 to 750 nanometers and is commonly associated with the color red. The term is used across several domains to indicate both a color and a signaling convention that prompts a particular action, such as stopping, caution, or attention.

In road traffic control, a red light is a universal signal to stop. Red signals are part of fixed-cycle traffic signals and are used to regulate vehicle flow at intersections, pedestrian crossings, and railway level crossings. In many jurisdictions, drivers must come to a complete stop before the stop line and may only proceed when the light changes to green or when directed by a traffic officer.

Red light is also used in lighting and imaging contexts because it interferes less with night vision than white light. This property makes red illumination common in astronomy observatories, certain laboratory work, cockpit and control-room lighting, and in photography or film when preserving ambient light sensitivity is important or when close observation requires minimized glare.

The phrase red-light district refers to urban areas associated with adult entertainment and prostitution. The name derives from the historical use of red lamps or signs to mark such districts; today the term is used descriptively and is subject to local regulations and debates about legality and public health.

Red light therapy, or photobiomodulation using red or near-infrared light, is explored for potential effects on skin healing and inflammation. Evidence is mixed and methodologic quality varies by study; red-light therapy is not a substitute for established medical treatments and should be used with professional guidance where appropriate.