Paul Dove via EV wrote:
Halogen bulbs are made in general for 6V, 12V, 24V... Using too low a voltage will produce little current and too high a voltage will produce high current and overheating of the filament
Actually, light bulbs don't behave like resistors. Ohm's law doesn't apply. :-)
A light bulb's apparent resistance changes drastically with temperature. The cold resistance (measured with an ohmmeter) is easily 1:10th that of its hot resistance (current divided by voltage at full rated voltage). Depending on the type of light, an 8-1 change in voltage only causes about a 2:1 change in current.
This means that light bulbs can be used as crude constant-current loads. The current only changes slightly despite large changes in voltage. This characteristic is ideal for testing batteries, where you'd like the current to stay the same despite changes in cell or battery voltage.
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