Luminous intensity can be measured in lux units (lux Lux), luminous flux units (lumens Lumen), luminous intensity units (Candlepower) 1CD (Candlelight), which refers to objects that radiate completely, one in sixty-tenths of a litre at the freezing point of platinum. The luminous intensity of the square centimeter area. (Previously referred to a 2.2-centimeter-diameter whale candle with a mass of 75.5 grams, burning 7.78 grams per hour, a flame height of 4.5 centimeters, luminous intensity in the horizontal direction) 1L (lumens) means 1 CD candle light irradiation at a distance of 1 cm, The luminous flux on a flat surface of 1 square centimeter. 1Lux means that the luminous flux of 1L is evenly distributed over an area of ​​1 square meter.
General active luminous body uses luminous intensity unit candlelight CD, such as incandescent lamp, LED, etc.; reflection or penetration type of object uses luminous flux unit lumen L, such as LCD projector, etc.; and Lux ​​unit Lux Luxus, generally used in photography and other fields . The three units of measure are numerically equivalent but need to be understood from different perspectives.
For example: If an LCD projector has a brightness (luminous flux) of 1600 lumens and its projection to a total reflection screen is 60 inches (1 square meter), its illumination is 1600 lux. Assume that the light exit from the light source 1 In centimeters, the area of ​​the light outlet is 1 square centimeter, and the luminous intensity of the light outlet is 1,600 CD. The true LCD projector will be greatly reduced in brightness due to the loss of light propagation, loss of reflection or transmission film, and uneven light distribution. Generally, 50% efficiency is good.
In actual use, light intensity calculations are often used in data units that are relatively easy to map or to change direction. For LED display screen, this active light emitter generally adopts CD/square meter as the luminous intensity unit, and cooperates with the observation angle as an auxiliary parameter, which is equivalent to the illuminance unit of the screen surface; and this value is equivalent to the effective display area of ​​the screen body. Multiplying to obtain the luminous intensity of the entire screen at the optimal viewing angle, assuming that the luminous intensity of each pixel in the screen is constant in the corresponding space, this value can be considered as the luminous flux of the entire screen. General outdoor LED display must reach the brightness of 4000CD/square meters or more to have ideal display effect under sunlight. Ordinary indoor LED, the maximum brightness of 700 ~ 2000CD / square meters.
The luminous intensity of a single LED is in units of CD with a viewing angle parameter, and the luminous intensity is not related to the color of the LED. The luminous intensity of a single tube varies from several mCDs to 5,000 mCDs. The luminous intensity given by the LED manufacturer refers to the point at which the LED is lit at a current of 20 mA, and the luminous intensity at the best viewing angle and center position is the largest. The shape of the top lens when the LED is packaged and the position of the LED chip from the top lens determine the LED viewing angle and light intensity distribution. In general, the larger the viewing angle of the same LED, the smaller the maximum luminous intensity, but the luminous flux accumulated over the entire three-dimensional hemispherical surface does not change.
When multiple LEDs are discharged in a more regular and regular manner, their luminescent spheres overlap with each other, resulting in a more uniform distribution of the luminous intensity of the entire luminescent plane. When calculating the display luminous intensity, according to the LED viewing angle and the LED emission density, the maximum point luminous intensity value provided by the manufacturer is multiplied by 30% to 90%, as the single tube average luminous intensity. General LED's luminous life is very long, manufacturers are generally marked as more than 100,000 hours, the actual should also pay attention to the brightness of the LED decay cycle, such as most of the UR red tube used for car taillights after a dozen to dozens of hours after the brightness Only half of the original.
The brightness decay period has a lot to do with the material process of LED production. Generally, the four-element LED with slower brightness attenuation should be used when the economic conditions permit.
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