On Sun, 15 Oct 2006 08:37:01 GMT, "HiC" wrote:

Looking to power a mini halogen bulb to do film capture. It would be great
if I could power it off the movie projector itself without having to get an
additional power supply. The socket for the projector reads slightly over
24v. However, the lamps it uses are 21v. Someone has stated that load is a
factor. Does that mean that the voltage needs to be higher than the bulb
rating or not necessarily?

The actual no load voltage will almost always be higher than the
under-load voltage - unless the power supply is regulated (most movie
projectors aren't regulated unless you have a theater projector)

Voltage ratings on incandescent bulbs have to be taken with some
skepticism. They are usually intended to be "nominal" ratings.

For instance, a 12 Volt bulb intended for auto use will spend most of
its life working at 13.8 or higher and the people that make the bulbs
know that and take it into account.

Likewise projectors. The 21 volt bulb may be intended to run at 21
volts or 24 volts - unless you see the manufacturers curves regarding
ambient temperature, color temperature of the light, voltage and life
expectancy you're just "whistling in the dark."

Sometimes a lower voltage bulb is used at a higher voltage - it
shortens the life, but puts out more light and puts out higher color
temperature light - so color renditioning may be better.

Likewise, under load, your 24 volts will almost certainly be lower
than 24V.

What I wonder is if this 24v bulb should work off the 24v socket on the
projector?

http://www.1000bulbs.com/product.php?product=685

Thanks

Get a 24 V lamp and try it. If you can't live with the color (should
be "warmer" -less blue) be happy and expect the lamp to last longer
than a 21 V lamp in the same application .



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