Green light for green LEDs!
Green light for green LEDs!
The first three-color, all-LED traffic lights started operating in October in Stockholm. The all-LED (light-emitting diodes) light reduces energy and maintenance costs by about 85 percent compared with standard traffic lights. Investment costs are still high, but are expected to drop during 1997.
The headline in IAEEL Newsletter 3-4 1995 "Sixty Percent Less Energy With LED Traffic Lights" is now obsolete.
With the green LEDs finally on the market, the potential savings is 85 per cent with today's LED signals, replacing a 70-W lamp with a 10-W LED disk. New LED technology and smarter optics for the distribution of light could cut power consumption to 8 W or less per signal. Arrows would only need 4 watts.
Rather than wait for an evaluation of field tests, Stockholm City's Street Department has already begun investing in all-LED technology. In the relay-to-microprocessor technology replacement program for traffic lights, all signals in poor condition are to be exchanged for LEDs.
It had been hoped that since LED lenses don't get very hot, dust would not stick to them, and consequently, rainfall would be enough to wash them clean. Field trials showed this assumption to be wrong, however. Nevertheless, if all 27 000 lamps, most of which are rated at 70 W, are replaced with LEDs the city should save appr. $850 000 annually in running costs, according to Lars Söder, at Stockholm Street Department. Since the LEDs last at least 30 times longer than filament lamps, long-term maintenance is reduced to a slight amount of cleaning.
Investment costs are still high, though. The price for a single signal (replacement of one lamp, complete with 230-V supply) is still as high as US$360 for the green, $260 for the yellow, and $175 for the red standard lights, according to Kalle Hashmi, project leader at the Department of Energy Efficiency at NUTEK, the Swedish Board for Industrial and Technical Development. But 1997 will see drastic cost reductions, Hashmi claims. For the red lights he predicts that prices will be $100-135 and "closer to $100". The green lights should come down by at least $50. As a result of the introduction of higher intensity diodes with better optics, the number of diodes used for each light can be reduced without causing the lamps to appear "dotty". Since fewer diodes are needed, total investment costs can be brought down.
By comparison, a 3-light signal head with 70-W lamps costs some $380 including lamps, and with halogen lamps some $470-500. 3-lamp traffic signals are not sold without lamps, so there are no list prices available for empty light head housings. But Sven Persson at Stockholms Entrepenad hopes that empty signal heads adapted for LED disks can be produced for $150. Today, there is only one supplier of green diodes in the world, Nichia in Japan, which, however, took the step from lab to production in less than two years. Other producers, such as Hewlett Packard, should start marketing their products in 1997.
"We have been informing road authorities throughout Sweden and in other Nordic countries concerning the benefits and availability of LED traffic lights. The more lamps we can get installed, the more we can cut their price, so it is in our own best interest to spread the word", says Lars Söder at the City of Stockholm.
Twelve hundred LED traffic lights are now on their way to various places in Sweden, with some destined as far north as the city of Luleå with a sub-arctic climate. In general, the all-LED lights are being delivered to the locations where red LEDs have been tested over the last couple of years. According to Sven Persson at Stockholm Entreprenad, the city's road construction company which is now distributing the new lights, there have been no complaints about the red ones. His organization has also designed a prototype of a flat housing for the lights. Such a housing should allow traffic lights to be leaner and less expensive. The other LEDs are placed in retrofitted standard housings.
The stipulated 520 nanometer green color has been achieved with a single type of diode, not by a mix of blue-green and yellow-green diodes, the possibility some observers foresaw in 1995.
More than a hundred green traffic lights, emitting the more blue-green Japanese standard, are already operating in the city of Fukuoka, where Nichia is producing them. Some green diodes are now also in place in Nuremberg, Germany, and some were installed in Canada and the United States during late 1996. Nichia is stepping up its production capacity, which is currently about 100 000 diodes. By early 1997, they hope to be producing 10 million diodes a month.
Fredrik Lundberg
Contacts at the City of Stockholm:
-
Lars Söder
Tel: +46 8 785 62 08
Fax: +46 785 62 90
- Sven Persson
Tel: +46 8 619 40 00
Fax:+46 8 619 43 50