CANDLE POWER :- The candle power as a unit of light intensity originally represented the horizontal intensity of light from the British Standard Candle, but since the value can be more accurately preserved and reproduced in the incandescent lamp. This arbitrary value is now maintained in tested incandescent lamps in the National Physical Laboratory, and in other countries. The unit of light in general use in Great Britain, France, United States and other countries (Germany excepted) is termed the "International Candle."

The relations of the International Candle to other terms are as follows:-

• 1 International Candle - 1 Pentane Candle (Great Britain)
• 1 International Candle - 1 Bougle Decimale or 0.104 Carcel Units (France)
• 1 International Candle - 1.11 Hefner Units (Germany)

MEAN HORIZONTAL CANDLE POWER (M.H.C.P.) is the average power given off in the horizontal plane of a lamp through the centre of the light.

MEAN SPHERICAL CANDLE POWER (M.S.C.P.) is the average of the candle power given off in all possible directions (i.e., at all points of a sphere surrounding the lamp).

LUMEN :- The Lumen represents the quantity of light falling on one square foot of the surface of a sphere of one foot radius from a light source of one candle intensity; placed at the centre of the sphere.

FOOT CANDLE :- The Foot-Candle is the illumination produced by a light flux of one lumen, uniformally distributed over an area of one square foot.

BRIGHTNESS OR INTRINSIC BRILLIANCY, is usually defined as candle power per sq. in. of projected area.

ILLUMINATION :- The unit of illumination is the Foot Candle.

FLUX OF LIGHT is measured in lumens, and is equal to the intensity of the illumination multiplied by the area over which it is distributed.

• M.S.C.P * 4π = Total Lumens.
• Foot Candles * sq. ft. = Lumens.

ENGINEERING SERVICE. The name Holophane stands not only for a product, but for a service made possible through a product. Engineering service in regard to the use of these refractors, or in regard to any street lighting problem will be furnished gladly, without charge, by the Street Lighting Department of Holophane Limited.

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