Light

Light

from Ching Viz Dictionary of Architecture

Light = Electromagnetic radiation that the unaided human eye can perceive, having a wavelength in the range from about 370 - 800 nm and propagating at a speed of 186,281 mi./sec

nanometer = A unit of length equal to one billionth of a meter, used esp. to express the wavelengths of light in or near the visible spectrum. Abbr. = nm

Angstrom = A unit of length equal to one ten-billionth of a meter, used esp. to express the wavelengths of radiation. Symbol: A

Ultraviolet = <>

Violet = ~370 nm (visible)

Blue

Green

Yellow

Orange

Red = ~800 nm (visible)

infrared = > 800 nm (non-visible)

luminous intensity = the luminous flux emitted per unit solid angle by a light source expressed in candelas

candlepower = Luminous intensity expressed in candelas

candle = a unit of luminous intensity used prior to 1948, equal to the luminous intensity of a wax candle of standard specification.

candela (Cd) = the basic SI (Systeme International) unit of luminous intensity, equal to the luminous intensity of a source that emits monochromatic radiation of frequency 540 x 10 to the 12th hertz and that has a radiant intensity of 1/683 watt per steradian. Also called a standard candle.

solid angle = an angle formed by three or more planes intersecting at a common point.

steradian (sr) = a solid angle at the center of a sphere subtending an area on the surface equal to the square of the radius of the sphere.

luminous flux = the rate of flow of visible light per unit time, expressed in lumens.

lumen (lm) = the SI unit of luminous flux, equal to the light emitted in a solid angle of one steradian by a uniform point source having an intensity of one candela.

cosine law / Lamberts law = the law that the illumination produced on a surface by a point source is proportional to the cosine of the angle of incidence.

inverse square law = One of several laws relating two quantities such that one quantity varies inversely as the square of the other, as the law that illumination produced on a surface by a point source varies inversely as the square of the distance of the surface from the source.

illumination / illuminance = the intensity of light falling at any given place on a lighted surface, equal to the luminous flux incident per unit area and expressed in lumens per unit of area.

lux (lx) = the SI unit of illumination, equal to one lumen per square meter.

foot-candle (FC)= A unit of illumination on a surface that is everywhere one foot from a uniform point source of one candela and equal to one lumen incident per square foot.

Luminance = The quantitative measure of brightness of a light source or an illuminated surface, equal to the luminous intensity per unit projected area of the source or surface viewed from a given direction.

Lambert (L) = A unit of luminance or brightness equal to 0.32 candela per square centimeter.

Foot-lambert (fL) = A unit of luminance or brightness equal to 0.32 candela per square foot.