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Terms used in lighting


Wattage (W)
The unit for measuring electrical power. It defines the rate of energy consumption by an electrical device when it is in operation. The energy costs of operating a device are calculated as its wattage times the hours of use. In single-phase circuits, it is related to volts and amps by the formula Volts x amps x PF = Watts (for AC circuits PF must be included).

Lumens (Lm)
A unit of light flow, or luminous flux. The lumen rating of a lamp is a measurement of the total light output of the lamp.

Lux (Lx)
A unit of illuminance or light falling onto a surface. One lux is equal to one lumen per square meter. Ten lux approximately equals one foot candle.

Candela (Cd)
Unit of luminous intensity, describing the intensity of a light source in a specific direction.

Color Rendering Index (CRI)
A scale of the effect of a light source on the color appearance of an object compared to its color appearance under a referenced light source. Expressed on a scale of 1-100, where 100 indicates no color shift. A low CRI rating suggests the colors of objects will appear unnatural under that particular light source.

Lumen Maintenance Ratio (LMR)
The proportion of the light output of a lamp after a stated period compared with initial lumen output.

Color Temperature (K-Kelvin)
The color temperature is a specification of the color appearance of a light source, relating the color to a reference source heated to a particular temperature, measured by the thermal unit Kelvin. The measurement can also be described as “warm” or “cool”. Generally, sources below 3000K are considered warm, 3000K-4200K is considered bright and those above 4200K are considered cool sources.


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