Photometry terms

Luminous flux 光通量 (phi)
The amount of light radiated by a light source per second, and the unit is Lumen (lm). Often used to specify the total amount of light emitted by a lamp. It does not specify the directions in which the light is radiated. 

Luminous intensity 光度 (I)
The amount of light that travels in certain directions from the source, and is measured in Candelas (cd).

Illuminance 照度 (E)
The amount of light falling on a surface is illuminance, and the unit is Lux (lm/m^2).

Luminance 亮度 (L)
The light is reflected off of surfaces and is measured in Candelas per square meter (cd/m^2).

[1] http://academy.autodesk.com/library/building-science/measuring-light-levels
[2] http://www.lighting.philips.com/main/connect/lighting_university/just_in_time_learning_videos_about_lighting/luminous-flux.wpd

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