Explanation of Luminous Intensity
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Explanation of Luminous Intensity

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1. Analysis of commonly used luminous intensity measurement units

The unit of measurement of the luminous intensity of the luminous body is:

1) Illumination unit: Lux

2) Luminous flux unit: Lumen

3) Luminous intensity unit: Candle power

Here first explain 1CD (candle light: Candela): refers to a completely radiated object, at the freezing point of platinum, the luminous intensity of every sixtieth square centimeter area.

Explain again 1Lux (lux): refers to the illuminance when the luminous flux received per square meter is 1 lumen. The relationship between illuminance, luminosity and distance is: E (illuminance) = I (luminosity)/r2 (distance squared)

Finally, explain 1L (lumens): the luminous flux of 1 CD candle light irradiated on a plane with a distance of 1 cm and an area of 1 cm 2.

2. LED luminous intensity units to dispel doubts

Active illuminants such as LEDs and incandescent lamps use candle light (CD) as the unit of luminous intensity. Luminous (L) luminous flux units are used for reflective or penetrating objects. The illuminance unit Lux is used in photography and other fields. These three units of measurement are numerically equivalent, but need to be understood from different angles. 

For example, the brightness (luminous flux) of an LCD projector is 1600 lumens. If it is projected on a 60-inch (1 square meter) total reflection screen, the illuminance is 1600 lux. Assuming that the light outlet is 1 cm away from the light source and the area of the light outlet is 1 cm2, then the luminous intensity of the light outlet is 1600CD. 

However, in fact, due to the loss of light transmission, reflection or loss of the light-transmitting film of the LCD projector, its brightness can generally reach 50% efficiency. In terms of current application experience, the outdoor LED display screen must have a brightness of more than 4000CD/m2 to obtain a more ideal display effect under sunlight. For ordinary indoor LEDs, the maximum brightness is about 700 to 2000 CD/m2.

Finally, it should be noted that the luminous intensity given by the LED manufacturer refers to the point where the LED is lit at a current of 20 mA, and the luminous intensity at the best viewing angle and the center position is the largest. In this way, although the luminous intensity of a single LED is in the unit of CD, its luminous intensity has no relationship with the color of the LED. Generally speaking, the luminous intensity of a single tube should range from a few mCD to 5000mCD.

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