to the fi lament. Th is is called the halogen cycle. Incandescent bulbs produce light using electricity to heat a metal fi lament until it becomes “white” hot or incandesces. HID lamps – also known as xenon lamps because they contain a trace amount of xenon gas – provide much better illumination, are more energy effi cient and last longer than a conventional incandescent headlamp – around 3,000 hours. HID lamps replace the fi lament within a glass tube of gas. Light is produced from an electric discharge that forms between two electrodes. HID lamps emit twice the light of halogen headlamps and produce a blue-white light. To get the better illumination, HID lamps have to be paired with a ballast which is used to regulate the high voltage supplied to the capsule of gas. Th ese lamps require special maintenance. It should be noted that potentially harmful materials are used in their construction. LEDS LED headlamps off er greater effi ciency, less heat generation, better light color performance and much longer product life. Th ey require very low power to work, are very durable and rugged and have lower cost over the life of the vehicle. A drawback of LEDs is that there is typically higher upfront costs. LEDs produce light very effi ciently by passing an electrical current through semiconductor material. LEDs are directional light sources, emitting light in a specifi c direction. LED lamps typically do not “burn out” or fail. Rather, they experience lumen depreciation. Th e lumen depreciation for LEDs is typically around a 7 percent reduction over 25,000 hours. It is not a major factor with LEDs, but in contrast, it is a major factor with halogen headlamps LEDs will last up to 30,000 hours and they use a very low voltage. Truck-Lite introduced the world’s fi rst LED custom headlamps for the commercial truck market in 2012. LED headlamps provide a much better view for the driver because the light emitted is in a color spectrum that provides high contrast and is more readily seen by the eye. Th is results in a much safer view of the road and a generally longer range of illumination. Th ere is a perception that LED headlamps are brighter because the light LEDs produce is more of a true white color. Traditional halogen headlamps that drivers are familiar with have a yellow-white hue. Industry experts describe the color of white that halogens produce as warm white. It contains a great deal of red, a small amount of green and very little blue. Th is helps a driver see stop signs, but they may not see other blue or green items. MAINTENANCE How involved is the maintenance and repair/ replacement headlamps? Halogen bulb replacements are very readily available, with well-established service methods. LED lamp assemblies are interchangeable, but the light sources or “bulbs” are not. LED bulbs are not legal for use in the U.S. Trucks that use proprietary headlamps versus sealed beam bulbs generally require dealer service because, in general, there are no lamps per se, but the LEDs are integral to the headlamp system. LED headlamps are designed to last the life of the vehicle, so they shouldn’t have to be replaced or repaired. Th ere is no bulb and the solid-state nature of LEDs means that they are nearly impervious to damage from shock and vibration. VEHICLE HEADLAMP technologies continue to evolve in form and function. Glare – defi ned as a bright light that interferes with vision – makes it diffi cult to see, plus is uncomfortable. This impacts a driver’s ability to properly see and that can make for a dangerous situation. Photo courtesy of DK Communications Vehicle headlamp technology has become increasingly more advanced, resulting in improved long-range visibility without causing discomfort, distraction and glare to the driver or others on the road. Photo from iStock Headlamp coatings Technological advances to the headlamps for commercial vehicles have resulted in longer headlamp life. That, obviously, is a good thing. But with it comes a serious problem that often isn’t given much attention: hazing, crazing/cracking and yellowing. Regardless of the type of headlamp, they have highly engineered, optically-based light patterns that are specially aimed to give the driver the best view of the road ahead, as well as to prevent discomfort glare to oncoming drivers. Today’s headlamps are made of hard plastic or polycarbonate resin, covered with a clear fi lm (coating) to protect the surface. Over time, through exposure, this protective fi lm wears away, resulting in hazing, crazing/ cracking and yellowing on the headlamp. These conditions negatively affect the headlamp by diffusing its light output for reduced visibility. To lessen the effects of headlamp hazing, crazing/cracking and yellowing, properly clean headlamps on a regular basis. COATINGS There are many coatings available on the market today for headlamps. Make sure, as you consider specifying LED headlamps, that you get a coating that will last as long as the LED light sources. The Technology & Maintenance Council (TMC) has a recommended practice – RP 171, High-Performance Coatings for Forward Lighting on Commercial Trucks – that provides guidelines for specifying coatings used on headlamps, fog lamps and driving lamps using plastic lenses that are used on commercial trucks. The intent is to increase headlamp service life, improve visibility and ehance safety. TMC (www.trucking.org/Technology_Council. aspx) is the only industry association that is focused solely on truck technology and maintenance. Contrary to some popular opinion, the headlamp restoration process does not return the lamp output to a like-new condition. The headlamps look better but do not produce the same output as a new headlamp. Continued Page 18 Heavy Duty | VehicleServicePros.com ❚ AUGUST 2016 ❚ FLEET MAINTENANCE 17
FleetMaintenance_August_2016
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