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Photometry Glossary

1.Flux
Definition: the sum amount of light emitted per second by luminous body, i.e. the luminous flux;
Shows: Symbol Φ, Unit lumen Lm;
Measuring method: When measured by luminous flux tester equipped with an integrating sphere or measured by photometer directly;
Applications: Represent the emitting energy in all directions on a lamp. The light output of one 40W fluorescent is approximately 2100Lm.

2.Light Intensity
Definition: the emitted light flux by a light-emitting body in a unit solid angle of a specific direction;
Shows: Symbol I, Unit candela cd;
Measuring method: measured by photometer directly;
Application: shows the light-emitting ability of a light-emitting body in a specific direction.

3.Illuminance
Definition: the luminous flux irradiated on the unit area of illuminated object by luminous body;
Shows: Symbol E, Unit Lux Lm / m2;
Measuring method: measured by photometer directly;
Application: If every square meter of the illuminated surface received flux 1Lm, then the illumination is 1Lx. The ground illumination on the midday of summer is about 5000 Lx, the ground illumination on sunny winter is about 2000Lx, the ground illumination of sunny Moonlight is about 0.2 Lx. And normal reading requires 300Lx or so.

4.Brightness
Definition: the luminous flux irradiated in unit solid angle per unit area by luminous body in a particular direction ;
Shows: Symbol L, Unit cd / m2;
Measuring method: measured by a luminance meter directly;
Applications: Evaluate the brightness of TV monitors and other surface-emitting body. The visual effects is better when the brightness ranged between 150cd / m2 and 350cd / m2.

5.Light Efficiency
Definition: The capacity of light source transformed electrical energy into light represent by divide flux emitted by the power consumption.
Unit: lumens per watt Lm / w;
Measurement Method: At first, measuring flux by flux tester, and then divide flux by the electric power, we can get the available light efficiency values.
Applications: The higher the luminous efficiency values, the higher of the ability for lighting equipment to convert electrical energy into light energy, namely, the stronger of the ability to save energy of energy-saving lighting equipment when provides the same brightness, and the stronger of the lighting for lighting equipment under the same power, i.e., the greater the brightness.

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