Proper Voltage
Since a well-designed 12v lighting system delivers a maximum of 12v and a minimum of 10v to the lamps, one would expect that the quartz-halogen lamps will meet or exceed the manufacturer"s "average lamp life" criteria. This ranges from 2,000 to 10,000 operating hours in theory; in practice, the life of a quartz-halogen lamp depends on operating voltage, manufacturing tolerances and cost: expensive lamps last longer.
Cost-benefit factors yield an actual average lamp life of 2,000 to 5,000 hours. Since an outdoor lighting system switched on from dusk to midnight accumulates a total of about 2,000 operating hours annually, lamp life can be accurately assessed. Some lamps will fail "early"; in the example above, 500 lamps failed during the test period to yield "average lamp life" for 1,000 lamps. Lamps operating at less than 12v but more than 10v last longer. Thus, if the voltage at each lamp is known, the failure rate (barring defective lamps) can be predicted.