Im confused. The announcer at the strip today kept saying that this guy cut a "perfect .500 reaction time". Now if reaction time is the time between the green light and the time the car begins to move (or trip the start timer) wouldn't a perfect reaction time be zero?

 

In the older days a perfect light was considered .000. The new timing systems can be setup to display the older system but most now accept a .500 Full tree as a perfect light.

With a full tree the 3 amber lights count down and the green light come on .500 seconds apart from each other. Your reaction time is a calculated number from the time the green light comes on to the time you break the starting beam. Because humans and cars have a delay time before reacting, racers time themselves to launch when they see the last yellow light come on. By the time you react and the car starts to move, .5 seconds can elapse. If you time it right the green light will come on a split second before the car breaks the starting beam. If you're too quick and break the beam before the green comes on you get a red light.

In reality, yes, it is a .000 reaction time but that makes it hard to show a bad light. If you red light, you get a .4xx reaction time or if it's really bad a .3xx reaction time. Showing a negative number reaction time is hard to do on the timeslips and scoreboard.

The Pro tree that you see with top fuel, funny car etc is setup different. All three yellow lights come on at once and .400 seconds later the green comes on. It even harder to cut a perfect light since there's very little anticipation.

Reaction times doesn't affect ET but a poor reaction time can lose a race. I had an 8 second reaction time once during a test and tune run. As soon as the last yellow light came on I launched and stalled the car. It didn't move forward to trigger the starting beam. I ratcheted the shifter back to neutral, started the car, ratcheted back to first and launched. 8 second reaction time and a normal pass down the track.

 

Cool. yeah I noticed the difference in the pro starting, I hadn't had it explained tho. So you are saying that there is a .5 second delay between each amber light and the last amber light and the green light right? So the reaction time they are showing is really the time between the last amber light and the time that the car breaks the starting beam right? If .5 is perfect then that means that you start just as the green comes on. If you have a .3 that means you started before the green comes on, and a .7 means you started .2 after the green comes on? Yeay I figured out the deal about the reaction time not affecting the ET but I still wanted to practice a good reaction time for the time im actualy in a head to head race.
thanks
see you at the track

 

You broke the starting beam at that time. Since there's a short distance between the stage light and the starting beam, the car can actually start moving before the green light comes on. Just as long as the beam isn't broken before the green comes on. If you deep stage, you reduce this distance. Front tire size can play a part in stage lights. A taller tire covers more ground and can block the beam more as you roll into them.