TOKYO -- As more traffic signals in Japan switch from incandescent to light-emitting diode lights, a problem has cropped up. Because the energy-saving LED lamps do not produce as much heat, snow sticks to them more easily, posing a safety hazard.

Police departments in 12 prefectures are testing various fixes. Manufacturers have yet to come up with a definitive solution, forcing police departments to improvise.

Twitter is lit up -- in a manner of speaking -- with complaints about useless, snow-covered signals. Said one: "We're in a snowy country. Why LEDs?" On a highway in the city of Toyama in December, Nikkei reporters saw LED traffic signals covered so completely in snow they appeared to be switched off.

The National Police Agency says LED traffic signals are becoming more common because they have a longer service life, use less energy and are brighter. As of the end of 2013 about 45% of Japan's traffic lights used LED lights. The trend is growing.

Too cool

Complaints from police and others have traffic-signal manufacturers racking their brains for a solution. In 2011, Nippon Signal and Kyosan Electric Manufacturing together introduced transparent, bowl-shaped covers for LED traffic signals.

The Ishikawa Prefectural Police installed the covers on signals in 10 locations. "They may be somewhat effective, but I saw snow piled up on the upper third of the cover," said a sheet-metal worker living in the city of Hakusan. The Tsurugi office of the prefectural police, located across from the light, occasionally sends officers to remove snow from the covers with long sticks.

Manufacturers are experimenting with changing the shape of covers, applying special surface coatings and the like, but it is still a question of trial and error. "There is no universal remedy because snow quality varies regionally," said an official at Kyosan.

Koito Electric Industries, based in Shizuoka Prefecture, has developed a "flat" traffic signal that has LED lamps mounted on a plate about 6cm thick. The signal is angled downward, rather than perpendicular to the road surface, to reduce direct exposure to snowfall. The Aomori Prefectural Police, which has installed these signals, reports improved visibility, but once the snow sticks, the colors are difficult to see. The police say the surface temperature of LED traffic signals is 20-29 C compared with about 45 C for conventional lamps.

The Yamagata Prefectural Police has introduced a system to melt snow off traffic signals using a heated wire. Fukuoka Prefecture-based Shingo Denzai installed the wires only on red signals. In heavy snow, however, the wires do not do the job completely. Police have asked the manufacturer to improve the system.

Aomori Prefecture has set up a working group that includes research organizations in the prefecture to develop its own system. "Developing a system that works is urgently needed to substitute for manual snow removal. If we succeed, we can expect demand nationwide," said the group's chairman, Akira Kudo of the Aomori Prefectural Police.

(Nikkei)