LED Power Supply

Traffic lights used low power LEDs for many years, but now some manufacturers are using a few high power LEDs instead. One problem with traffic lights is controlling the wavelength of the yellow (amber) light. Yellow LEDs suffer from a greater wavelength shift than other colors, and this may cause them to operate outside their permitted spectral range. Another problem is driving them to fail-safe-authorities permit some degree of failure, but if more than 20% of the LEDs fail, the entire lamp must be shut down and fault reported to maintenance teams.

High ambient temperatures inside the lamp housing can lead to LED power supply failures. This is particularly true if the LED power supply contains electrolytic capacitors, which vent when hot and eventually lose their capacitance. Some novel LED power supplies have been developed that do not need electrolytic capacitors and can operate for several years at high temperatures. Failing LED power supply can give LED lights a bad name- Why have LEDs that can work for over 100,000 hours if the LED power supply fails after 10,000 hours' operation?

Street lights have been built using medium and high power LEDs. Although this would seem to be a simple application, high ambient temperatures and relatively high power LEDs can give rise to power supply problems. In some cases, white and yellow LED lights are used together to create a "warm-white"? light. The problem with white LEDs, made using a blue LED and a yellow phosphor, is that the high blue content produces a "cold-white" light.