[ELECTRON] Power / current in a lamp

[Clive Mitchell]

12V lamps I guess?  It's more likely to be 0.3A and not mA.

The 0.3A (300mA) is the current drawn at the rated voltage and the
3.5W is the total power dissipated, part of it being light and part of
it being heat.

Tungsten lamps are a bit more complex than that though.  They have a
positive temperature coefficient which means that they start off with
a much lower resistance than when they are running, so they can draw a
pulse of high current at turn-on.

The efficiency falls off rapidly at lower voltages, but the life goes
up exponentially.  Likewise when over-run the efficiency increases,
but the life is shortened dramatically.

On 11 May 2010 17:33, Seb Bacon <seb.bacon at gmail.com> wrote:
> On our wee lamps, it says 0.3mA, 3.5W.  What does that mean?  That the
> lamp performs most efficiently at that current and power?



-- 
Clive Mitchell.

http://www.bigclive.com