Illuminance

Illuminance is the luminous flux incident on a surface per unit area, measured in lux. It describes how much visible light reaches a surface, weighted by human visual sensitivity.

Luminous flux: Luminous flux is the rate at which visible light, weighted by human visual sensitivity, is emitted or transferred. Illuminance divides incident luminous flux by the receiving surface's area.
Inverse-square law: The inverse-square law states that intensity from a point source decreases with the square of distance. For a point source, illuminance falls with distance squared when orientation is fixed.
Lighting design: Lighting design plans the placement, intensity, and character of light in built environments. Designers calculate illuminance to meet visibility and comfort targets across surfaces.
Luminance: Luminance measures light emitted or reflected from a surface per projected area and solid angle. Illuminance describes incoming light; luminance describes light leaving toward an observer.
Lux: The lux is the SI unit of illuminance, equal to one lumen per square metre. It expresses illuminance as luminous flux per unit surface area.
Cosine law of illumination: The cosine law of illumination states that surface illuminance decreases with the cosine of incidence angle. A tilted surface receives less flux per area than a surface facing the source.
Daylight factor: The daylight factor is the ratio of indoor illuminance from daylight to simultaneous unobstructed outdoor illuminance. It compares interior illuminance with the available exterior daylight.
Luminous intensity: Luminous intensity is luminous flux emitted per unit solid angle in a given direction. It characterizes a source directionally, rather than the flux reaching a surface.
Lumen: The lumen is the SI unit of luminous flux, weighted by the human eye's sensitivity to light. A lumen measures the light amount counted in illuminance.
Lambert's cosine law: Lambert's cosine law describes the angle-dependent emission or reflection of an ideal diffuse surface. It governs how Lambertian surfaces distribute reflected light relevant to illuminance.

Linked from 17 pages