High-Power, Short-Wave LED Purifies Air

Brent D. Johnson

Ultraviolet radiation has numerous applications in the decontamination of a variety of materials. It has been used effectively for groundwater filtration, sterilizing of foodstuffs and cleaning of semiconductors. Ultraviolet decontamination systems typically employ xenon, mercury or quartz flashlamps, but Toyoda Gosei Co. Ltd. of Heiwa, Japan, has developed a compact air purifier based on its TG Purple Hi LED.

An air purifier based on ultraviolet LEDs is finding a place in numerous applications, including in the passenger compartment of the Toyota Mark II and Premio vehicles. The device is built into the roof between the driver and passenger seats.

The primary difference between this system and an active-carbon air purifier is that the organic materials are decomposed rather than adsorbed. The TG Purple Hi features GaN on a sapphire substrate in a 320 X 320-µm flip-chip structure and produces more than 10 mW at 20 mA. The 385-nm LED irradiates titanium oxides dispersed on grains of carbon within the purifier to produce OH radicals and oxygen ions that break down the organic materials that cause bad odors into CO₂ and H₂O.

The system also eliminates more serious organic compounds. For example, acetaldehyde and toluene are common components of automobile exhaust. Exposure to these chemicals can produce skin and respiratory tract irritations and nervous system disorders. After 20 minutes of operation, the LED air purifier decomposes 80 percent of acetaldehyde and 95 percent of toluene, vs. 10 and 95 percent for an active-carbon system.

Accordingly, Toyota Motor Corp. has incorporated the ultraviolet system into the passenger compartment of its Mark II and Premio vehicles. Daikin Industries Ltd. and Mitsubishi Electric Corp. also are using it in home air-conditioning units and refrigerators, respectively.