terms and definitions

COLOR REDUCING INDEX (CRI)

A scale from 0 -100 used by lamp manufacturers to indicate how normal and natural a light source makes objects appear in full sunlight or in incandescent light. Generally, the higher the CRI, the better it makes people and objects appear

ballast

a circuit component in flourescent and HID lighting fixtures that provides the required voltage surge at startup and then controls the subsequent flow of current through the lamp during operation

starter

a circuit component of certain flourescent lighting fixtrues that is used to heat the lamp electrodes before the lamps are lighted

luminaire

a complete lighting unit including the lamp(s),wiring, support, protective covering, and ballast(where applicable)

lumen maintenance

a measure of how a lamp maintains its light output over time. It may be expressed either numerically or as a graph of light output versus time

lumens per watt (LPW)

a measure of the efficiency, or, more properly, the efficacy of a light source. The efficacy is calculated by taking the lumen output of a lamp and dividing by tthe lamp wattage. For example, a 100w lamp producing 1750 lumens has an efficacy of 17.5 lumens per watt

diffuser

a part of a lighting fixtrue that redirects or scatters the light produced by the fixture lamp to provide diffused lighting

troffer

a recessed lighting fixture installed with the opening flush with the ceiling

reflected light

light reflected from an object that does not have self luminating properties but relects light provided from another source

diffused lighting

lighting on a work surface or object that is not predominantly incident from any particular direction

dip tolerance

the ability of an HID lamp or lighting fixture circuit to ride through voltage variations without the lamp extinguishing and cooling down

lumen (lm)

the basic measurement of light. One lumen is defined as the amount of light cast upon one square foot of the inner surface of a hollow sphere with a one-foot radius with a light source of one candela in its center

refracted/refraction

the bending of a light wave or ray as it passes obliquely from one medium to another of different density, or through layers of different density in the same medium

reflected

the bouncing back of light waves or rays by a surface

work plane

the distance above the floor where a task is to be performed. In offices and schools, this is usually 30". In kindergartens, it would be lower, and in some manufacturing areas, it would be much higher

candela(cd)

the international system unit of luminous intensity. It is roughly equal to 12.57 lumens. The name has been retained from the early days' of lighting when a standard candle of a fixed size and composition was used as the basis for evaluating the intensity of other light sources

incident light

the light emitted from a self luminous object such as the sun or an electric source

efficacy

the light output of a light source divided by the total power input to that source. It is expressed in lumens per watt (LPW)

luminance

the luminous intensity of any surface in a given direction per unit area of that surface as viewed from that direction. Measure in candela/m2. The term luminance is commonly used to express brightness

candlepower(cp)

the measure of light intensity measured in candelas(cd). It is used to indicate the intensity of a light source in a given directino. The higher the intensity of light, the more candelas it represents and the higher the candlepower.

Incandescence

the self-emission of radiant energy in the vvisible light spectrum resulting from thermal excitation of atoms or molecules such as occurs when an electric current is passed through the filament in an incandescent lamp

glare

the sensation produced by luminance within the visual field that is significantly greater than the luminance to which the eyes are adapted

lux

the standard international unit of illuminance and is equal to one lumen per square meter

footcandle (fc)

the unit used to measure how much total light is reaching a surface, such as a wall or table. One lumen falling on one square foot of surface produces an illumination level of one footcandle. One footcandle also equals 10.76 lux