In NHRA pro starts, green appears 0.4 seconds after the amber lights flash. This simultaneous-amber launch is called a professional, or “pro,” tree.
The Christmas tree starting system uses staging beams to determine when both cars are positioned. Once the race-start sequence begins, all three large amber bulbs illuminate together. Drivers must react during the brief interval before green; leaving the starting beam too early produces a red-light foul.
The timing differs from an NHRA sportsman, or full, tree. In that format, the three ambers illuminate sequentially, with half-second intervals, followed by green. That longer visual countdown makes the two systems easy to confuse.
Reaction time is measured from green illumination until the car leaves the staging beams. It is separate from elapsed time, which begins when the vehicle leaves the starting line and ends at the finish. A strong reaction can therefore help a driver win even when the car itself records a slower elapsed time.