WASHINGTON (AP) -- Patients with a certain type of acne can soon opt for light therapy to try to clear it up.

The Food and Drug Administration approved a device Monday that emits high-intensity light to help clear up moderate inflammatory acne.

The ClearLight system doesn't work on severe acne or mild cases of pimples but works only on inflammatory acne, which is caused by bacteria, said Neil Ogden, FDA's director of general-surgery devices.

The theory is that the light kills the bacteria inside the pimples.

It's blue light, a different wavelength than skin-damaging ultraviolet light, and thus is thought to cause no side effects, he said.

Israel-based Lumenis Inc. studied about 48 patients with moderate inflammatory acne, treating half the face with the ClearLight and comparing the result with the untreated other side of the face, Ogden said.

The treatment consisted of eight twice-a-week, 15-minute light sessions.

Not everyone responded. If the acne does not seem better after two or three sessions, there's only a 10 percent chance it will respond to the treatment at all, Ogden said. About half of the patients who finished all eight treatments saw at least 50 percent decreases in the number of pimples, he said.

Acne patients have a range of options, from topical ointments to antibiotics and, for the most severe cases, drugs like Accutane. That drug can cause severe birth defects, however, so it's used under very strict precautions to treat young women. ClearLight would offer a subset of acne sufferers - Lumenis estimates up to 13 million - a nondrug alternative.

The company estimates patients would pay about $50 a session, or $400 for a full course of treatment. It's not clear how often recurrent acne sufferers could undergo light therapy.

Lumenis said it would begin shipping the light device to dermatologists immediately. The company would not disclose how much the machines will cost doctors.

Copyright 2002 The Associated Press. All rights reserved.