control led by PWM module

We are know that PWM(pulse width modulations) is normal technology for control led . but there are has some body is not clear which work principle . All right, we want to do one more at simple PWM example here.

We are put the a second divided into pieces of one thousand . a pieces of work time is one millisecond . then we will make that led lit one for 7 millisecond and lit off for 3 millisecond through led controller . in this sense, the led only work for 0.7 second in one second . due to there was a faster interval for state transition, so our eyes can not found led flash.all we saw was about the light is rather dim.

Through this way , we can be control led bright.