LED lamp for old projector

[D.M. Procida]

I have an old transparency projector (SVE Picturol Model Q,

). It currently has a 100W B15 bulb, but I am not thrilled by the wiring arrangement and would prefer to run it with a low-voltage lamp.

This is the existing bulb and holder:

. There are low-voltage drop-in B15 LED lamps available (12-36V), but I can easily replace the holder if another type would be more suitable. I don't need

100W equivalent, but I don't think I want to go below 800 lumens or so.

The projector has a focusing mirror behind the lamp, and I don't know how much difference it will make to use a lamp that blocks more light than the original bulb.

Thanks for any advice.

Daniele

[Brian Gaff (Sofa]

Well it makes quite a bit of difference, and also can affect the way colour looks on bothmovies and transparencies.I'm out of the loop since losing my sight of course, and led technology has moved on, but that was what was being talked about in the year 2000. Brian

[Dave W]

Forget it. In my old slide projector the lamp is a 150W tubular all glass wire ended and has has a horizontal filament maybe 5mm long, and the reflector forms a real image of it just above, so the lens sees both the filament and the image to get double the light from the lamp alone.

I see your projector is much older, but the reflector still produces an image of the filament superimposed on the filament. B15 refers to the size of the holder, not the bulb. The only LED bulbs I can find have long linear 'filaments', so although the reflector will still produce an image (assuming a clear glass bulb), the light source is much bigger and the projector lens can only make use of the area the original filaments occupied.

[Theo]

Would something like a halogen car lamp bulb work? That can be run off 12V

- you'd obviously need to replace the fitting. But the light pattern out of the sides might be roughly similar, if you got one without a reflector inside the bulb.

Doing it with LED, I think you'd need something with a very focused beam - like those LEDs used in torches or bike headlights. That's not something you'd see in a mains bulb apart from perhaps GU10s and similar. To the OP, try searching ebay for 'Cree' which should pick up a number of examples - a popular brand, although most of those listed are probably not made by Cree.

You'd need your own mounting for these, of course. And watch for thermals, since they may need more cooling than the big original bulb did. (despite being lower wattage, the heat is more concentrated)

Theo

[Paul]

I gather there are three options at least.

Some of the lasers from projection systems have been repurposed to make laser pointers, but perhaps those aren't exactly eye-safe. You can even overdrive the lasers taken out of a CD/DVD/BR player for stuff like that.

If you play around with an array LED, it's best if it is already on an alumina substrate, so you can fasten a heatsink to the back of it directly. The high power LEDs I bought (so-called at the time), they came soldered to alumina "Star" substrates, making electrical connection to them a lot simpler to do.

This is an example of a high power device, where the manufacturer was kind enough to put alumina on the back. The only question is how you solder the two wires to it. If it really puts out 7000lm, that's probably on the order of 70W, and that's on the order of 55W of heat to remove. The heatsink will require forced air cooling. The only way it wouldn't need forced air, is if you butt a series of heatpipes to the back of the array instead and use an array of passive coolers on the end of the heatpipes.

Paul

[Thomas Prufer]

The filament is imaged? and tricky to replace, I'd think.

Perhaps using a LED with a COB -- i.e. a flat light-emitting surface?

*I* would dig out my rechargeable workshop light with a COB LED (15 mm x 20 mm or so), remove the optics from the projector. Then hold the optics in front of the COB and play around to see if it could possibly work in terms of light output, and shape and light distribution of the COB. If it's at all reasonably possible, then buy a COB, heatsink, and constant current driver, and bodge it all together. Possibly using the base of a broken bulb as a mechanical holder. (ISTR that some projectors had screws to move the bulb filament around...)

Thomas Prufer

[Animal]

fix the wiring :) Bulb run cost is not going to see any significant improvement by going LED. It would if it were on 8 hours every day.

[D.M. Procida]

I was finally able to do some experimenting. First I removed the rear reflector, and tried an LED spotlight through the aperture where the reflector was, and then a 12V 50W halogen spotlight.

The halogen spotlight was better, but neither was remotely satfisfactory. The pattern of the diodes or the spotlight reflector in each case were very visible in the projection.

I also tried a 12V 50W GY6.35 halogen bulb more or less in place of the orginal 100W bulb. That was best, but still not as good as the original, and there still seemed to be some shadow of the bulb in the image.

Daniele