How the Christmas tree works
The Christmas tree is the starting device between the two lanes of a drag strip. According to NHRA 101, each side has small pre-stage and stage lights at the top, three large amber bulbs, a green bulb and a red bulb. Pre-stage lights up when your front tires are about 7 inches behind the starting line, stage when they are on it. Once both cars are staged the tree comes down, in one of two ways:
| Tree | Ambers | Green | Used in (NHRA) |
|---|---|---|---|
| Pro (.400) | All three flash together | 0.400 s after the ambers | Heads-up classes, from Top Fuel to Pro Mod |
| Sportsman, or full (.500) | One after another, 0.500 s apart | 0.500 s after the last amber | Handicap classes such as Stock, Super Stock and Top Dragster |
The NHRA glossary defines reaction time as the time from the green light to the front tires clearing the staging beam, with .000 as a perfect reaction time. Leaving before the green is a foul start, shown by the red light, and usually loses you the round.
Practicing on this tree
Pick Sportsman or Pro above the tree; the page remembers your choice. Click the tree, tap it or press Space to stage: the pre-stage and stage bulbs light, and after a random wait the ambers come down. Press when you want to launch. Your light appears the way a time slip shows it:
- .043: you launched 43 thousandths of a second after the green came on.
- .000: a perfect light, exactly on the green.
- −.006: 6 thousandths too early, a red light. Pressing before the ambers even start is a red light too.
The last ten runs are listed under the tree, reds included, with your best legal light. Your best light is kept on this device, and Share result shares a light with the tree it was cut on.
Timing the tree, not reacting to it
A simple reaction to a light takes most people around 0.2 seconds or more in a browser test, so waiting to see the green gives a light of .200 or worse. The ambers are what you time from: the green always comes 0.500 s after the last amber on a full tree, and 0.400 s after the flash of all three on a Pro tree. Here your press is the launch, so a perfect light means pressing exactly that long after the amber, and your own reaction time to the amber uses up part of the gap. Aim for the same light run after run: once your launch is consistent, a better light can win you a holeshot, NHRA’s term for a round won with a slower elapsed time thanks to a quicker start.
Your screen and your car
This page times the green from the moment the last amber reached your screen, and measures your press against it, so a slow screen, mouse or keyboard makes every light later. Practice on one device to keep your numbers comparable. In a car, the time it takes to clear the staging beam after you launch is added, so on a real tree you’ll need to launch earlier than here.
For a start you react to rather than time, try the F1 start lights or the classic reaction time test. Using a controller in a racing game? Check its buttons with the controller tester.