LED luminous flux is an indicator of a whole luminance of the light source. Unit is LM (Lumen). Frequently used in the light source for luminance, it is refer to the human eye’s sensitivity (visual acuity) to represent the physical quantities of light radiation brightness. A specific value for isotropic luminous intensity is 1cd light source in 1 sr (stereo radians) solid Angle of radiation flux is 1 lm. The sr is the unit of solid angle, says the intercept area where from the surface of the ball to its center as radius (r) 2 of cone apex Angle.
The light intensity is a index of luminous flux solid angle density. The unit is cd. Usually used in the glare of LED. It is defined as: Emission 540×1012Hz (555nm wavelength) frequency monochromatic light, in the specified direction of light emission intensity for 1/683W/sr light source, in the direction of the light intensity is defined as the 1CD.
Luminance is the intensity index from light source and surface reflection and transmission surface two times the light emitted by the light source to the observer. The unit is cd/m2. As with the luminous flux, is a physical quantity with the sensitivity of the human eyes. Mostly used in the LCD panel and PDP display screen luminance.
Illuminance is an indicator of the luminance of the light exposure to the plane. The unit is LX (Lux), sometimes labeled as lm/m2. It refers to the light source exposure into luminous flux of the planar object, per unit area’s luminous flux, and used for comparison of the bright light exposure to the plane.
The relationship of luminous flux between light intensity, luminance and illuminance are briefly summarized as follows: Divided by the flux per unit solid angle is equal to the intensity; divided by the flux per unit area is equal to the intensity of illumination, intensity divided by unit of area equal brightness.