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luminous intensity 

Date: 20120321 
The definition of luminosity

Brightness  that symbol I, unit candles (cd)
Luminosity is a particular direction angle of light within the amount of radiation per second, that symbol is I, while the unit is the candle (cd). Luminosity can be defined as: a particular direction horn emitted volume (flux).
As a result, will give us the solid angle and its "steradian steradian" unit concept; the solid angle is from one vertex of the cone surface and is surrounded by the metric space out.
In general, the light beam radiation is not evenly in all directions, but the projection to a particular direction; assumptions, we imagine that a narrow angle of the cone where the apex is a light, let the average beam and projected out The beam is a small hole through the projected extension of the solid angle and form a cone, the intensity of the light source on the known brightness (I), its unit is the candle (cd), the center line of the cone is the light source direction.
Steradian solid angle to measure the A Steradian is a measure for a solid angle Solid angle as the size of the angle or radian plane angle; imagine a random radius (r) of spherical and contains a vertex as the center of the cone, this small halfsphere surface is surrounded by the cone and the cone should be solid angle (w) formed; if this small halfsphere surface area is equal to the square radius (r2), which corresponds to the solid angle was called "steradian steradian", we assume that the small surface area is not equal to half the sphere radius square (r2), the area will be equal to A, and this solid angleSteradian.
The sphere will contain the 4p steradian A whole sphere contains 4p steradians Solid angle will be the largest covers an entire sphere, and a surface area of sphere radius r is 4pr2, this solid angle will be equivalent toSteradian; so half of the sphere will contain 2p steradians steradian.
The concept of the luminosity is very important in lighting technology, as a general lighting equipment is not projected in all directions evenly. This part should be very prudent and careful handling; when speaking to the viewer some perspective projection is more important, other extra light on the need to avoid . Therefore, the brightness of lamps for projection light source or plan, arrange appropriate projection direction of light projection range will enhance efficiency.
Bicycle without reflector headlights, no specific direction projection 
2,5cd Candlelight 
Bicycle reflector headlamps with, set light projection 
250cd Candlelight 
Incandescent reflector bulb (jewelry lamp> PAR38E Spot 120W, set of light projection 
10 000cd Candlelight 
Lighthouse center beam, set light projection 
2 000 000cd Candlelight   

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