On Sun, 10 May 2009 19:27:16 +0100, "N_Cook" put
finger to keyboard and composed:

N_Cook wrote in message
...

I measured a projector that has 300W consumption on the mains plate but no
info for the bulb consumption.
Added 0.1R in the supply line to the bulb gives an inferred reading of 2.8
amp and 80V over the lamp after 10 minutes to warm up , so 224 watts seems
about right.

Interesting the brightness setting is just in the DLP chip , not the lamp.
But selecting "low power" option does reduce the light output but with
lamp
volts staying at 80V , so presumably current draw is less, (0.1R
disconnected by then). This option for reduced fan noise , if large
display
/ high ambient light useage, is not required

I'd forgotten about the hook-up wire volts drop, about 145W, 80 volt, 1.8
amps for the lamp. DC that is of course

It seems to me that your lamp has a constant voltage characteristic
and that its brightness is determined by a variable current source
within an electronic ballast.

I would think that the arc voltage would be determined by the lamp's
geometry. For example, could it be possible that one maker's 100W lamp
A may be rated for 1A at 100V, whereas another maker's lamp B may be
rated for 1.25A at 80V? If so, then a ballast designed for lamp B when
used with lamp A may try to deliver a constant current of 1.25A,
causing the lamp to dissipate 125W.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.