Marker lamps are frequently fitted to the outside of large vehicles, such as trucks, trailers, and recreational vehicles. Marker lamps are installed on a vehicle to provide an indication of its size, shape, and direction of motion so that nearby motorists and pedestrians can quickly evaluate the characteristics of the vehicle and take necessary steps to avoid an accident. Some vehicles, such as large trailers, are provided with a set of top located marker lights, known as clearance lights. Clearance lights are mounted on a vehicle in order to provide a ready indication of whether or not the vehicle can drive under a low ceiling structure, such as a bridge or a loading dock canopy. A typical marker lamp assembly comprises an incandescent light bulb that is encased inside a small housing. A colored lens, typically an amber lens, forms the outer wall of the housing. The amber wavelength light emitted by the bulb passes through and is diffused by the lens. This light is the light nearby motorists and pedestrians observe when they see an illuminated marker light.
While conventional bulb-in-housing marker lamps have proved useful for providing an indication of the shape of the vehicle to which they are attached, they are not without some limitations. The trucks, trailers, and other vehicles to which these lamps are mounted often experience intense vibrations and/or vibrate constantly while in motion. The bulbs in these lamp assemblies contain thin, fragile filaments. Over time, the vibrations to which these bulbs are exposed cause the filaments to break, resulting in burnout of the bulb. Since many marker lamps are located on the top of the vehicle to which they are attached, and can be 10 or more feet off the ground, removing and replacing the burned-out bulbs can be a laborious and time-consuming task. Another disadvantage of these assemblies is that in some environments the ambient light may be so intense that it washes out the light emitted by a marker light. This can make it difficult on a bright, sunny day, for example, to use the marker lights to evaluate whether there is sufficient clearance for a truck trailer to pass under a bridge or through a tunnel.
Moreover, the housing forming the body of a marker lamp is simply a hollow body. The outer wall of this body is a thin plastic layer that has relatively minimal mechanical strength. Consequently, the lenses of this assembly are prone to breakage when struck by foreign objects, such as rocks that may be thrown up from the road by the wheels of the vehicle or deliberately thrown by mischievous persons. Once an object breaks the lens, the lamp assembly may no longer emit the appropriate color light and confuse nearby persons who expect the light to have certain characteristics. Also, if the object strikes the marker/clearance light hard enough it will break not only the lens but the bulb inside the lamp housing. Once this happens, the lamp assembly is rendered completely useless.
Recently, there have been some attempts to use light-emitting diode (LED) lamp assemblies to substitute for conventional incandescent bulb-type marker lamps. A disadvantage of these assemblies is that a single LED does not emit light over a relatively wide arc. In order to provide an LED marker lamp assembly capable of emitting light over a wide viewing field, it has been necessary to construct these assemblies using a number of spaced-apart LEDs. These assemblies are typically too large to put in a vehicle body opening that are normally formed to accommodate marker lights. Moreover, the large number of LEDs that form a single lamp assembly collectively typically consume a relatively large amount of power.