In a drag race drivers must wait until the green light is illuminated before they can move their vehicle explain why the time delay exist?

The delay that exists in drag race drivers shows the human reaction time which is being compared with the anticipated green light.
In drag raising, we have break-out where a car runs quicker the dial-in while delay box is an electric device which is an aid to the driver.
The driver adjusts his reactions by changing his number in the delay box whereby he sets brake on just one set by line-lock.
Reaction time indicates the amount of delay from the last yellow light which is being turned on. 500 indicates that green light it is the perfect light and if delayed below 500 it shows that the car started moving before the green light.