LED die for 8mm projector conversion

[Daravon]

I just bought a very solid BOLEX 8mm projector; the film transport seems to work but the light doesn't. The light bulb is some crazy looking thing that's silvered all over except for a spot facing the film gate.

I'm hoping that I can replace the bulb with an LED, but I'm not sure how much power I need. I have some older 1-watt luxeon dice around, but do you think I will need something gnarer? Is this even possible to replace a powerful incandescent with one LED?

Also, I guess projectors just used tungsten light because that's what was available, but do you think color films' color balance was tuned to incandescent light and using an LED is going to mess everything up?

 

[MikeAusC]

Because filaments radiate light in all directions, projectors used complex optics to focus the light on the tiny 8mm film image - spherical reflector and two big collimating lenses.

LEDs focus the light inherently in one direction so I would tsrip out all the optics and put the LED directly behind the film.

An SST90 LED has a large area close the size of 8mm film so I would start with that.

You won't be able to use it at full power - 30 watts - but running an LED at less lower makes it more efficient.

 

[Yoda4561]

Not sure what your level of technical expertise is, but I'd have to recommend against this unless you have a good background in optics or are willing to settle for a poor quality result. Lamps for those old projectors are less than 30 dollars it seems. http://www.super8stuff.com/lamps.html . I just don't think it would be worth the effort and possibility of ruining something like that bolex. If you do go ahead with it, an SST90 LED or similar output class (1500+ lumens) will probably be required, and a warm one would be helpful. It's also likely that collimation of the SST90 or any LED will be required, as they emit a 120+ degree beam by nature, too wide to get proper screen brightness. If you can nail the collimation a 50 watt halogen (which is what I think you have) puts out some 500-600 lumens, so you may be able to get away with something like an SST50 or the upcoming cree XM-L. Some tungsten bulbs have coatings to artificially raise their CCT, so you may be able to get away with a 4500k LED, but a cool white would likely ruin the tonal balance of the film. Integrating the heatsink, LED driver, and optical kung-fu is likely to prove difficult, so don't start it if you're easily discouraged.