Light barrier
Also: Photocell, Timing beam
A light barrier takes your time when your car breaks a beam of light across the road, often to the hundredth of a second.
A light barrier is a timing device that records the moment your car breaks a beam of light across the road. The sender and the receiver stand on either side of the road.
Where you meet them
Many organisers use light barriers for the start, finish and intermediate times of a regularity test. They often measure to the hundredth of a second. A light barrier hidden in a hedge is part of a secret check.
What actually triggers it
The first part of the car to cross the beam triggers the time. On most cars that is the front bumper. Depending on how high the beam is set, another part may get there first. That is a difference to a pressure hose, which reacts to the front wheel.
Practical tip
If you want to hit a known light barrier on the second, keep your speed steady right up to the line. Braking or speeding up just before the beam usually adds more error than it fixes. Our guide to timing methods compares light barriers, hoses and GPS.