# What is light,luminous flux, illumination ?

What is light?

Light is a form of energy, which is radiated by heated bodies. The light is the part of the radiant energy which produces a sensation (of light) on the human eye.

What is luminous flux ?

Luminous flux is the light energy radiated per second from a luminous body in the form of light waves. It is measured in lumen.

What is lumen ?

Lumen is the unit of luminous flux which is equal to the flux emitted per unit solid angle from a uniform source of one candle power.
1 lumen = 0.0016 watt (approx).

What is luminous intensity ?

Luminous flux emitted by the sources per unit solid angle in any particular direction is known as the luminous intensity.

What is illumination ?

The luminous flux falling per unit area on a surface is known as illumination and is expressed in Lumen/m2.

What is a standard candle ?

A standard candle is that weighs 1/6 pound of pure spermaceti wax and burning at the rate of 120 grains per hour i.e. 7.776 grams per hour.

What is a standard candle power ?

The light coming out from a standard candle used as the unit of illuminating power of a lighting source is called standard candle power.

What are foot-candle and metre-candle ?

Foot candle or Lumen per square foot is defined as the illumination produced on the inner surface of a hollow sphere of a hollow sphere of radius one foot by a point surface at the center of intensity of one candela.
Metre-candle or Lux (Lumen/m^2) is defined as the illumination produced on the inner surface of a hollow sphere of radius one meter by a point surface at the center of uniform intensity of one candela.

What will be the total flux emitted by a source of 60 candle power ?

Total flux = (4 π × total candle power) Lumens = ( 4 × 3.1421 × 60) Lumens = 754.2 Lumens

What do you mean by M.H.C.P ?

Mean Horizontal Candle Power ( M.H.C.P) is the mean of the candle powers in all directions in the horizontal plane passing through the source of light.