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 are a blue LED light set, 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 bulbs. At this point, with most modern starting lights, the tree is activated. Once pre-staged, drivers roll up 7 inches and cross the second beam on the starting line, bottom bulbs, Once the first driver activates the bottom bulbs, the subsequent drivers have seven seconds or they are timed out and automatically disqualified, even in qualifying (a red-light foul is ignored in qualifying). Once all drivers have crossed the staged sensor or are timed out, the automatic starting system will activate the next lighting sequence within 1.3 seconds of the last car being staged or being disqualified. 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