Liquid Crystal Film Protects Against Flash Blindness

"Continuous, non-damaging, but blinding glare is a problem for drivers, welders, optical sensors and communications equipment," says Dr. I.C. Khoo, professor of electrical engineering. "This material can protect both people and equipment from flash blindness."

The material is a sandwich of liquid crystal between two sheets of glass. The researchers mixed the liquid crystal material with a very small amount of a dye -- methyl red -- which enhances the low intensity light stopping ability of the liquid crystal.

Liquid crystals can protect against glare and even laser flashes because they respond to light intensity nonlinearly. As the intensity increases, the liquid crystal lets in dramatically less light. In the past, Khoo used this property to create an optical switch that reacts in a fraction of a nanosecond to a damaging laser intensity by shutting out the light.

However, for some applications, it is necessary to protect against continuous, long term light that is below the level that will permanently damage the human eye or optical sensors, but intense enough so that seeing through the glare is impossible. That is where the liquid crystal optical limiting film has potential applications.

"A welding robot's optical sensors are blind while they are welding," Khoo told attendees today (Dec. 2) at the annual meeting of the Materials Research Society in Boston. "It would be helpful if some vision was available during the actual process."

The sun also creates a glare problem that conventional sun glasses cannot solve and human welders are forced to wear very dark eye protection. Both these applications require that the operators have some vision.

With the advent of lasers, communications satellites and other optical sensors need protection against damage by intense laser light, but they also need protection against intense, continuous light flare or dazzle which can occur both accidentally and intentionally in the form of laser jamming.

"The optical limiting film can reduce light with the intensity of 140 milliwatts to only 5 microwatts," says Khoo. "This is a dramatic reduction in intensity and sufficient to solve the glare problem. The liquid crystal material has a very large dynamic range."

Besides potential use as eye and sensor protection, this liquid crystal can also be used in photographic systems to enable photographers to take pictures even if intense glare would normally fog the film or create light streaks. Khoo believes the material has other applications in image processing as well.

"Some liquid crystals present themselves as promising next generation image processing and optical switching/limiting materials," says Khoo.

Khoo's work is sponsored by the U.S. Army Research Office, the U.S. Air Force and the Naval Air Development Center.