good rule of thumb to remember is, if a light is on avehicle, the light must work and be safe.Lamps and BulbsTrucks and buses are lit up like Christmas treeswhen operating at night. In addition to the headlightsand taillights, which are the minimum running lightsrequired bylaw for all vehicles operating at night, trucksand buses must also have clearance and side markerlights. These lights outline the length, height, and widthof the vehicle.Each group of lights in a branch circuit of thelighting system is protected by a fuse or circuit breakerand is provided with a switch. Each light in the groupis provided with one or more light bulbs that are ratedfor the particular circuit.Light bulbs used in Navy equipment are made tooperate on a low-voltage current of 12 or 24 volts,depending upon the voltage of the battery system used.Bulbs are rated as to size by the candlepower of lightthey produce. They range from small one-halfcandlepower to large 50-candlepower headlight bulbs.The greater the candlepower of the bulb, the morecurrent it requires when lighted. Bulbs are identified bya number on the base.Operators are responsible for replacing burned-outbulbs on equipment.Manufacturers have designedbulbs with such a wide variety of designs (fig. 4-4) thatit is impossible to list all the bulbs here. A bulb designcommonly used has either single or double contacts withnibs to fit bayonet sockets, as shown in figure 4-5.Because of some unique designs, certain bulbs have tobe handled with care; for example, quartz bulbs shouldnot be touched by the oil in your skin, because the oilcauses the bulb to fail instantly. Because of the uniquecharacteristics of the various bulbs, you should checkthe operator’s manual before replacing any bulbs.The sealed beam light is actually a large bulb (fig.4-6). The bulb consists of a lens, filaments, and a glassreflects. Sealed bulbs also have various designs; somehave filaments designed for high beam, some with onefilament designed for low beam, and bulbs with twofilaments designed for high and low beam.Clearance LightsClearance lights detail the maximum width of thevehicle, not necessarily its height as the word clearanceimplies. These lights highlight the protruding unlightedfront and rear corners of the vehicle that are subject toFigure 4-4.—Bulbs.Figure 4-5.—Single- and double-contact bulbs.collision with other vehicles or persons, not the top ofthe vehicle. Clearance lights should be mounted at aheight best suited to allow them to be readily seen froma minimum distance of 500 feet from the vehicle. Theclearance light on the front of a vehicle should be amberin color, and those facing the rear red. Some stateregulations require that larger vehicles have identification4-4
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business