Light Emitting Diodes (LED) have been used in the trucking industry for various purposes for over 20 years. However, many people still consider them to be “new”. LEDs are now being used for any of the exterior lighting, including...
November 1, 2011
Chuck Carman; curriculum developer, CARS
Light Emitting Diodes (LED) have been used in the trucking industry for various purposes for over 20 years. However, many people still consider them to be “new”. LEDs are now being used for any of the exterior lighting, including the white forward lighting.
When current crosses the PN junction of a typical silicon diode, heat is created. A LED, instead, uses various mixtures of elements like gallium, phosphorus and arsenic to produce different colors of light, including white, when current crosses the PN junction. Producing white light is done in one of two ways. One method is to use three LEDs where each produces one of the three primary colors (red, green and blue) and then combine the colors to produce white light. The other way is to use phosphor which converts a blue light into a white light. LEDs appear brighter than incandescent bulbs since they produce a monochromatic light—only one shade of a color.
LEDs are a solid state electronic device with no moving parts, so there is no coil filament to vibrate and break or short and open the circuit. This is, in part, why they are able to last so long. In many cases, the lamp will last the lifetime of the truck. Incandescent bulbs have a life expectancy of as little as 1,500 hours while a LED may last for 100,000 hours of operation.
LEDs provide a number of advantages over traditional lighting. They draw considerably less current than incandescent bulbs. For example, two incandescent stop lamp bulbs may draw approximately 4.2 amperes while the comparable LED assemblies will draw approximately 1.0 ampere. Two incandescent tail lights may draw 1.2 amperes but a pair of LEDs may draw as little as 0.15 amperes. This drop in required current puts much less strain on the truck’s electrical system. Another benefit is that manufacturers can use the same LED to function as a tail lamp and a brake lamp—they just need to feed the LED more current to produce a brighter light and act as the brake lamp.
LEDs allow for more light (lumens) from a smaller assembly. Reducing the size of the light assembly allows for greater flexibility in design and a reduction in overall material used. LED advancement has further improved over the years—where 70 LEDs were originally used in combination stop/tail lamps assemblies, they can now be produced using only three. Some manufacturers are introducing new flexible paper-thin LED lights that can be applied with adhesives and follow the contour of most surfaces. These products can be produced using about 2% of the material used in producing a standard LED lamp assembly, while still meeting the same CMVSS/FMVSS photometric specifications.
One of the common concerns with the use of LED lighting is the lack of heat on the lens cover which assists in the winter months to keep the lens clear of ice and snow. Some light manufacturers have added thermostatically controlled heating elements to the lens cover that activate when the temperature drops down to the freezing point to assist in the winter months. Others state that the more intense light produced by the LED is able to shine through most accumulations of snow and ice.
LEDs do in fact produce heat (just not as much as an incandescent bulb) — this needs to be properly managed. Heat can damage a LED, reducing its available light output. Many LED assemblies, especially white forward lamps, produce so much heat that the casings must be made of metal rather than plastic and have large heat sinks attached to properly dissipate heat from the internal circuits.
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