Christmas tree (drag racing)

Modern drag races are started electronically by a system known as a Christmas tree. A common Christmas tree consists of a column of seven lights for each driver or lane, as well as a set of light beams across the track itself. Each side of the column of lights is the same; from the top down, there is one blue LED light set arranged in a circle with a white line through the center, then three amber bulbs, then a green bulb and a red bulb. The light beams are arranged with one set on the starting line, and another set 7 inches behind it.

When drivers are preparing to race, they first cross the beams 7 inches behind the starting line. Crossing this beam activates the top half of the circle. Once pre-staged, drivers roll up 7 inches and cross the second beam on the starting line, bottom half of the circle, including the crossing line. Once both drivers have crossed the staged sensor, an official starter or automatic starting system will activate the next lighting sequence.

After this point, the lighting sequence will be different based on the type of tree and start that a race is using. The "Standard" tree will light up each large amber light consecutively with a .500 second delay in between them, then followed by the green light after another .500 second delay. A "Professional" tree will light up all of the large amber lights simultaneously, and then after a .400 second delay, light up the green light. Some classes will use a hybrid tree, known as a .500 Professional tree, where the delay is .500 seconds instead of the .400 seconds used in a standard Professional tree. On the activation of the green light from either style of tree, the drivers are supposed to start the race. Leaving the "Staged" line before the green light activates will instantly stop the count down and result in a lighting of the red light and a provisional disqualification of the offending driver in heads-up starts only. In a Professional Tree or a Standard Tree with a heads-up start, if both drivers leave before the green light activates, only the first to leave will be charged with a provisional disqualification. In a Standard Tree with staggered start times, a green light will be shown to the first driver, regardless if he jumped or not, and once the second driver takes the start, if one driver jumped the start, then that driver's lane will display the red light. If both drivers jump, only the driver whose infraction was worse will be shown the red light, as if it was a heads-up start. If the driver that did not active a red light in his lane commits a further foul during the run (crossing a lane boundary or hitting the barrier), and the driver who commits a red-light foul does not cross a boundary line, the red light violation is overturned and the driver who crosses the boundary line is disqualified, with the driver who committed the red-light foul winning the round.

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Wikipedia