Thursday, January 12, 2012

Lighting background

Importance of light:

    Light is the prime factor in the human life as all activities of human beings ultimately depend upon the light. Where there is no natural light, use of artificial is made. Lighting increases production and reduce accidents.

 Basic Definitions:

Candela
International unit (SI) of  luminous intensity; term evolved from considering a standard candle, similar to a plumber's candle, as the basis of evaluating the intensity of other light describe the relative intensity of a source .

Candlepower Distribution Curve
A graphic presentation of the distribution of light intensity of a lamp or luminaire.

Illuminance (E)
The quantity of light (measured in foot-candles, Lux, etc) at a point on a surface.

Inverse Square Law
Formula stating that illumination at a point on a surface varies directly with the intensity of a point source, and inversely as the square of the distance between the source and the point; it illustrates how the same quantity of light flux is distributed over a greater area as the distance from the source to the surface is increased.

Light Loss Factor
The product of all considered factors that contribute to a lighting system's depreciated light output over a period of time, including dirt and lamp lumen depreciation.

Lumen
The international unit of luminous flux or quantity of light.

Luminaire
A complete lighting unit consisting of a lamp (or lamps) together with the parts designed to distribute the light, position and protect the lamps, and connect them to the power supply. This is sometimes referred to as a "fixture".

Lamp efficiency
It is the amount of output lumen per watt.

Lux (lumen/m2)
SI (international system) unit of illumination. One lumen uniformly distributed over an area of one square meter.

Mounting Height
Distance from the bottom of the fixture to either the floor or work plane, depending on usage.

Spacing to Mounting Height Ratio
Ratio of fixture spacing (distance apart) to mounting height above the work plane. Sometimes it is called spacing criterion.  A normal range is 1 à 1.5

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