The Unit and Calculation of Brightness
The Unit of Brightness:
1.1 Brightness unit are generally cd/m2, Lux and FL( foot-lamberts). We mainly use this unit cd/m2, when we order the resistance. For example, if we say that the required brightness is 5000. So here the unit of 5000 is cd/m2. Prepare light table use mcd as unit, like green LED 2000mcd.
1.2 Conversion calculation between units of the Brightness
nits and fL conversion formula: 1nits x 0.2919=1fL and 1fLx3.426=1 nits [Note: this factors is exported by pi(p) and m2/ft2(0.0929)]. ( nits is cd/m2) 1 nits =1000mcd.
People generally know that as long as we know the brightness of led lamp, then the brightness of LED screen can be calculated out. But there is difference between the calculated brightness and the actual brightness. We can roughly calculate.
2.1 the calculation of Pixel density
Firstly we need to know the pixel pitch of the LED module that we will produce.
We use P20mm outdoor LED screen as an example.
Pixel density calculated formula is :(1000 mm ÷ 20mm)×(1000 mm ÷ 20mm)= 2500/ m2
2.2 According to prepare light table, we can know the brightness of LED lamp as follow:
Red LED: 550mcd. Green LED: 2000mcd Blue LED: 350mcd
2.3 We know the pixel configuration of P20 mm LED screen is 2R1G1B.
2.4 We know that the ratio of white balance is R:G:B=3: 6: 1
2.5We can calculate out what brightness LED screen we can produce according to the above conditions. Using green light as an example
2000mcd*2500/1000 = 5000cd
So the brightness of the green light is 5000cd/m2, when its operating current is 20mA. Then we can calculate out the brightness of P20mm led screen is 8333cd/m2.
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