IIRC, the simple way to wire an led is with a series resistor chosen
to give the rated current at the expected voltage. The LED itself has
a very small resistance - as you would expect given its power
efficiency. Most of the power is then comsumed by the resistor.

Controlling the current by a more efficient means would involve a
complicated bit of circuitry.

Andy Repton writes:


The LEDs are themselves need between 1v and 4v depending on colour,
the 12v replacement bulbs must have some sort of internal drop down.
You need to check their spec to see if they can cope with the charging
voltage, but also to see if they can deal with the spikes etc that an
alternator based 12v system can produce.

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Andy Repton

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