Lower Voltage

The lifetime of the currently available white LEDs is not anything near the 100,000 hours of mono color LEDs. More typically it is about 5,000 to 30,000 hours at 20ma. The lifetime is related to how hot the junction gets during operation. As a result it is highly recommended that one design for half current or 10 ma to gain a significantly longer lifetime. Optimum design for a number of different input voltages was chosen based on limiting the LED current for the highest voltages that could occur during operation. The following table gives the different battery configurations chosen. AA is assumed to be a typical fully charged Ni-Cad or Ni-MH cell or a typical alkaline cell that averages in operation about 1.2 volts. It is assumed the cells are not being charged while the unit is in operation. A high of 15 volts for the typical 12 volt lead acid battery is assumed to be maximum charging voltage. In this case it is assumed that charging occurs during operation of the lighting. The following table shows the assumed voltages for design purposes.

	Volt for each Cell	Volt for 4-AA Cells	Volt for 8-AA Cells	Volt for 12 volt Battery
Low	1	4	8	11.5
Average	1.2	4.8	9.6	12.5
High	1.6	6.4	12.8	15

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