One is to change the current flowing through the LED, LED tube generally allows continuous working current of 20 mA or so, in addition to the red LED is saturated, the other LED brightness is basically proportional to the current flowing through; another way is to use Human visual inertia, using pulse width modulation method to achieve grayscale control, that is, periodically change the optical pulse width (ie, duty cycle), as long as the repetitive lighting cycle is short enough (refresh rate is high enough), people Eye is not feeling pixels glittering.As the pulse width modulation is more suitable for digital control, so commonly used microcomputer to provide LED display content today, almost all of the LED screen is the use of pulse width modulation to control the grayscale of.
Another method is the scan board serial transmission is not the content of each LED switching signal but an 8-bit binary brightness value. Each LED has its own pulse width modulator to control the lighting time. Thus, at In a repetitive lighting cycle, each pixel requires only 4 pulses at 16 levels of grayscale and 8 pulses at 256 levels of grays, greatly reducing the serial transmission frequency. With this decentralized control LED Grayscale method can easily achieve 256 gray-scale control.