A laser that stops traffic? Yes, a new light tool called "driver defeat" will help soldiers slow approaching cars from a distance so they can determine if the driver is friend or foe. It works like this; when a laser is pointed at the eye, the flashes create an "afterimage," an optical illusion that limits a person's sight for a very short time. It's a little like driving into the sun, says Gordon Hengst, a research physicist at Brooks City Air Force Research Lab. So, "if somebody's driving a vehicle the natural reaction is to either slow down or stop," giving soldiers that extra moment they need. Scientists are experimenting with the color, power and timing of flashes to make the laser a safe -- as well as effective -- universal stop sign.