The next time you stop at an intersection, take a closer look at the glowing red light. If it looks like a honeycomb of bright red dots, you are enjoying an example of LED traffic lights. Cities around the world have been systematically replacing their older incandescent bulb-based traffic signals with the more energy efficient LEDs since the mid-1990s. These traffic signals have several advantages over incandescent models, but the three main advantages are improved visibility, longer shelf life, and lower energy costs.
The development of commercially feasible LED traffic lights was originally hampered by the limitation of Light Emitting Diodes (LEDS). LEDs generate light as a result of electrical current running through certain gases. At first, LEDs could only produce the color red, which limited their use to monochromatic devices such as alarm clock displays or calculators. Further refinements in the technology have now produced the three colors used for traffic signalling: red, amber and green.
One major advantage of these traffic lights is increased visibility. Incandescent bulbs were often covered by color filters, reflectors, and glass lenses, which could affect how much light actually reached drivers' eyes. LED traffic lights use an array of bright LEDs that do not require additional filters or amplification. If a single incandescent bulb burns out, the entire light sequence is disturbed. Several LEDs can fail in these lights without causing a noticeable disruption. A catastrophic failure involving all of the LEDs in a panel would be rare indeed.
Another advantage is lower maintenance costs. Almost all of the cost of LED traffic lights are upfront — LEDs are expensive, and the signals themselves require more labor to produce. These expenses are usually offset by lower maintenance costs. If an incandescent bulb burns out, which happens three times a year on average, a trained city employee must replace the bulb while traffic is diverted. LED lights, on the other hand, may only require a yearly cleaning of the protective lenses. The individual light panels often last ten years or more, depending on the conditions.
On a related note, another advantage of LED traffic lights is noticeable energy savings. A standard incandescent lightbulb may use 100 watts of electrical power to produce light, but an equivalent LED panel uses 15 to 20 watts to achieve the same intensity. Considering how many thousands of incandescent lightbulbs must be lit around the clock, it is easy to see why LEDs are so appealing to cities on tight energy budgets. Larger cities can save substantial amounts of money by switching to LED traffic systems. Some cities that have converted still maintain an incandescent amber light, since it does not remain lit for as long as the green and red signals.