Lighting systems (Units of Light)
Color Rendering Index
CRI
Transparent
Capable of transmitting light so that bodies situated beyond or behind can be distinctly seen
Color Rendering Index
Difference between natural & artificial light/color; Lower CRI, bigger difference
Luminous intensity
Intensity of a light source that can be estimated by human eye; Also called as illuminating power; Luminous flux emitted from the source per unit solid angle; expressed in *candela* (Cd)
Lux
SI unit of illumination; lumen per *sq. meter*
Lumen
SI unit of luminous flux (lm)
Refraction
The change of direction of a ray of light as it passes obliquely from one medium into another in which its velocity is different
Law of reflection
The principle that when light or sound is reflected from a smooth surface, the *angle of incidence is equal to the angle of reflection and the incident ray*, the reflected ray, and the normal to the surface all lie in the same plane
Luminance
quantitative measure of brightness of light source
Illumination
*intensity of light* falling at any given place on a lighted surface; light flux density Also called as *Illuminance*; expressed in lumens per unit of area
Candela
basic SI unit of *luminous intensity* Also called, *standard candle* (Cd)
Specular
directed from a smooth, polished surface
Foot-candle
Unit of illumination on a surface equal to *lumen per sq. foot* (FC)
Opaque
impenetrable by light; not reflecting light
Incandescence
light from heat; emission of visible light by a body when heated to high temperature
Candlepower
luminous intensity expressed in candelas
Luminous flux
the *rate of flow of visible light* per unit time, expressed in lumens
Diffraction
the modulation of light or sound waves as they bend around the edges of an obstacle in their path
Reflectance
the ratio of the radiation *reflected* by a surface to the total incident on the surface
Reflection
the return of light rays from a surface
Incidence
the striking of a ray of light or sound wave on a surface
Transluscent
transmitting and diffusing light so that bodies on the opposite side are not clearly visible.
Foot-lambert
unit of luminance *per sq ft*; unit of brightness (fL)
Lambert
unit of luminance *per sq. centimeter* (L)
Candle
unit of luminous intensity used prior t 1948
Efficacy
*Lumen per watt* How well light source produces visible light
