Soon cops' flashlights might not only temporarily blind bad guys: they might also stop them in their tracks by disorienting them and making them nauseatingly sick. When suspects turn away or reel, cops or border-security agents can nab and handcuff them.

The flashlight, which is being developed for the Department of Homeland Security (DHS), uses a range finder to measure the distance to the target's eyes so that it can adjust the energy of the light to a level that won't cause permanent damage. Then it rapidly shoots out pulses of light from an array of ultrabright light emitting diodes (LEDs).

The flashes incapacitate a person in two different ways, says Robert Lieberman, CEO of Intelligent Optical Systems, based in Torrance, CA, which is making the device. The flashes temporarily blind a person, as any bright light would, and the light pulses, which quickly change both in color and duration, also cause what Lieberman calls psychophysical effects. These effects, whose effectiveness depends on the person, range from disorientation to vertigo to nausea, and they wear off in a few minutes.

It's not clear why the changing light pulses cause this effect, even though the effect has been well documented, Lieberman says. Helicopter pilots, for example, have been known to crash because they get disoriented by the choppy flashes of sunlight coming through the chopper's spinning blades.

The DHS is funding research on the new nonlethal weapon. According to a DHS press release, cops, border-security agents, and the National Guard could be armed with the new flashlight by 2010. The device is part of a larger effort to develop nonlethal weapons that can help law-enforcement and military personnel control crowds and riots, both in antiterrorist actions and in hostage situations.

The LED flashlight comes with a few caveats. The person being targeted could easily look away, or he or she might be wearing heavily tinted glasses. And the device would not be useful to, say, a security agent who is chasing a suspected attacker. "It is designed to be used on someone coming at you," Lieberman says. Also, the flashlight's effects are less during the day. But Lieberman notes that security agents will more likely face situations in which they need the device at night.

Glenn Shwaery, who researches nonlethal technology at the University of New Hampshire, says that authorities would use the flashlight, and other light-based "dazzler" technologies, to distract a suspect so that they can close in on him or her. "If you disorient or distract somebody and cause them to look away, then they can't focus on their task, which could be aiming a weapon at someone, or looking at a screen with sensitive information, or dialing a phone," he says.

There have been efforts to make dazzlers using lasers, but LEDs could be a safer choice. "Getting an eye-safe wavelength with a laser has been very difficult," Shwaery says. Because laser beams are energetic and focused, they could cause permanent damage to the eye. Shwaery adds that the new LED flashlight would be safe because it uses a range finder and adjusts the energy it throws out. "The ideal goal for nonlethal technologies is that they be scalable."

Researchers at Intelligent Optical Systems are now analyzing combinations of wavelengths and light intensities that have the strongest effect on people while remaining safe. They also need to make the device smaller and easier to carry. Right now, it's about 15 inches long and 4 inches wide. This fall, the team plans to test the flashlight extensively on people at Penn State University's Institute of Non-Lethal Defense Technology.