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1. Luminous Flux
As the measure of the perceived power of light, luminous flux differs from radiant flux, the measure of the total power of light emitted. The reason for that is luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. Lumens= (radiant flux) (630lm per watt) 1lm=1cd·sr. For example, for ordinary 40W fluorescent lamp, luminous flux is 2200 lumens, 100hours. So flux of 1W power domestic incandescent light produced is about 12.5lm (4tlm).

2. Luminous Intensity
As a measurement of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle,luminous intensity is based on a standardized model of the sensitivity of the human eye. Candela (cd), an SI base unit, is the unit. Because a candle's luminous intensity is about 1cd, value of domestic 100W incandescent is approximate about 100cd.

3. Illumination
The meaning is the luminous flux per unit area. So the meaning of surface illumination is an indication of light illumination degree. The unit is lux (Lx).

4. Brightness
As an attribute of visual perception in which a source appears to be radiating or reflecting light, brightness is the perception elicited by the luminance of a visual target. The unit is candela per square meter and the symbol is cd/㎡. 1cd/㎡=1nt Bennett.

5. Light effect
Light effect, also called light-emitting efficiency, is the ratio of light flux and power consumption. The unit and symbol is lm/W. Light effect of straight fluorescent light is about 30 ~ 60lm/W and incandescent bulbs' luminous efficiency is about 7 ~ 20lm/W. So it is evident that fluorescent lamps are more energy efficient than incandescent lamps.

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