In message ,
doozer wrote:

As someone who has worked with optics for projectors, I can tell you
that it won't work. You need an immense amount of light intensity and it
has to be focused just so (if you've ever fired up the projection lamp
with the housing open, you will know just how bright it is - you can't
see anything else for a few minutes). Many man hours of research go into
producing efficient optics for the projection beam. The lamps are
discharge (arc) types and have control gear in the projector - you can't
just replace them with any old lamp.

What you can sometimes do is buy the lamp itself separately, as the
manufacturer replacement often includes the reflector and housing. This
can cut down the cost considerably. Find the manufacturer code from the
lamp itself and google for it.

Hmmmm, that bodes badly then.

The bulb and reflector come as a single unit (see links below) so I
imagine the majority of the cost is in the bulb. I can't help getting
the feeling though that I'm being massively ripped off and its the
housing not the bulb that is expensive. I wouldn't be at all surprised
to find that practically every Philips projector uses this exact same bulb.


Many lamp replacement "kits" also include new (air) filters and possibly
other bits, so you have to include them in your comparisons too.

Went through this loop a few years ago with bulbs for NEC and BARCO
projectors. The Barco ones were £450 and had a rated life of just 720
hours. You could reset the warning up to 750 hours but after that the
projector put a big banner over the screen until you entered the serial
number of the new bulb. Actually, any old number would do, but since
these projectors were well over £15k new we didn't chance it.

We discovered that both the Barco and the NEC lamps (IIRC, certainly
the Barco ones) were simply re-packaged standard Osram bulbs, but at a
higher power rating than available through any of the usual outlets. I
forget the specifics, but we could get the bulbs up to (say) 250W, and
the Barcos needed 400W which were only available through Barco. Again,
needless to say, the bare bulbs were a fraction the cost of the
replacement lamp assemblies.

Eventually we managed to bulk-purchase the bulbs (we had 12 of the
Barcos IIRC, on 8+ hours a day) and got them at £250.

The NECs were better at £350 to start with (they came down too) and 2000
hour life. We had 16 of those.

*If* we could have got hold of the right sort of bulb we would have
tried it, BUT:

As for the light being focused. Yep I agree that it is focused but, and
here's the interesting bit, there is obviously a reflector in the bulb
but there is also a lense in front of the bulb that diffuses the light.
I am wondering just how accurately I would have to mimic the real bulb
to get a good solution.


The additional problem with the Barcos was bleaching of the dichroic
filters. No, I don't know how you can bleach a diffraction device
either, but they seemed to do that quite regularly, especially if the
projector had been apart for any reason (cleaning beyond the air filters
for example). It is just possible that if it wasn't put back together
absolutely perfectly a "hot spot" would develop. The dichroics were £150
each, again IIRC. With a DIY cobbled-together lamp assembly I suspect
that the problem would have been even worse.

This is still a problem with projectors. Yes, you may be able to get a
basic SVGA model for £500 from the right place, but if you are doing
more than watching a couple of hours of television in the evening you
really need to think about the running costs.

I think there might have been a slight misunderstanding as well. I
wasn't intending to just stick a low voltage halogen into the hole
occupied by the PJ bulb as I realise that wouldn't be even close to good
enough and wouldn't work anyway. I was thinking more like a dozen in an
internally mirrored and forced air cooled box that sits under the
projector with a mirror array to take the light into the PJ. Surely that
would be bright enough!

Have you ever *seen* the light from a discharge lamp? Ignoring the
problem of UV exposure (they produce gallons of the stuff) they have to
be the brightest source I've seen, Watt for Watt.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
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