LED displays are mostly driven by pulse width modulation, and gray levels are represented by different pulse widths. Therefore, the LED emission state is always the same, and the gray level is represented by the length of the luminescence.
Formula (1) is the color coordinate calculation formula of LED, X, Y, Z is three stimulus value, t is the luminous time, LED through the pulse width modulation gray level, the luminous time t determines the gray scale size, from the formula (1), no matter how gray level change, its color coordinates remain unchanged.
There is a linear relationship between the gray level and the XYZ three stimulus value and the time t. When the total gray scale series of LED display is N, the XYZ three stimulus value corresponding to each gray level step "1" is as follows:
The gray value of LED, N and M is three, XYZ, K, respectively: