This is topic bulb substitutes - LED? in forum 8mm Forum at 8mm Forum.

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Posted by Jon Byler (Member # 3933) on September 23, 2013, 02:06 PM:
Are there any out there? This seems like the ultimate way to replace old hard to find projector bulbs, but I'm not sure the power density is there yet. Lots of light, not much heat.

I was thinking about this for a way to replace the bulb in my bolex 18-5 when it eventually goes. it's too small for a standard MR16 bulb, and the smaller MR11's only seem to be available in about 30W size, which may be more than adequate moving from regular incandescent to halogen.
Posted by Janice Glesser (Member # 2758) on September 23, 2013, 02:23 PM: might want to pm Richard Bock from this forum. He sent his Bolex 18-5 somewhere to have it converted to run a lower cost halogen bulb.
Posted by Jon Byler (Member # 3933) on September 23, 2013, 02:35 PM:

I'll check with him to see what bulb it uses now. I'm still interested in the possibility of LEDs just out of general curiosity.
Posted by Bill Brandenstein (Member # 892) on September 25, 2013, 11:28 AM:
Maybe for general illumination, like a threading bulb. But LED technology hasn't come to the point of being able to focus a massive amount of light on a tiny aperture. Halogens still win for best light for the lowest cost.
Posted by Janice Glesser (Member # 2758) on September 25, 2013, 04:54 PM:
LEDs are great for telecine work where low wattage is a must... but as Bill states not for image projection.
Posted by Pete Richards (Member # 2203) on September 25, 2013, 05:33 PM:
There are LED light sources for digital projectors available, it is conceivable that you could use one of those in a film projector, but it would take some work.
Posted by Janice Glesser (Member # 2758) on September 25, 2013, 07:16 PM:
You are correct Pete...but aren't those projector lamps much larger? Maybe someday a smaller higher wattage LED will be available to adapt to film projectors.
Posted by Bill Brandenstein (Member # 892) on September 26, 2013, 11:47 PM:
You would need a lens to focus the light onto the aperture. But the luminous flux rating might be comparable to 100w or 150w Halogen - if you can harvest the light, that is.
Posted by Jon Byler (Member # 3933) on September 27, 2013, 12:02 AM:
that is something I have been curious about. I've seen some led chips that claim to be good for well over 700 lumens. that's pretty bright if all of the light makes it though the gate.

is the ideal situation one where one has columnated light that is all getting through the aperature in the film gate? I imagine much of the light from a halogen is wasted bouncing around in there when you have upwards of a 2 inch reflector and an 8mm hole. What presents itself as the ideal projection light source in terms of beam and focus? does the light need to be focused on the film plane itself?

I'm having a hard time finding the answers to these questions...
Posted by Bill Brandenstein (Member # 892) on September 28, 2013, 11:07 PM:
I'm no expert in this but think there's a great deal of wasted light in most any projector situation. Halogen bulbs lose a few percent through the dichroic reflector, more through the front angles untouched by the mirror, and around the top and bottom of the aperture. When you think of how much light comes from a 60w halogen car headlamp, where little light is wasted, you gotta think those projectors create a pretty inefficient situation!

But Jon, I'm sure you're right about one thing: yes, the light is focused on the film plane to whatever extent the technology permits. Halogen bulbs have a "working distance" for the mirror focus and you'll see that figure in bulb specifications.
Posted by Jon Byler (Member # 3933) on September 29, 2013, 06:03 PM:
Thanks for the reply. I'm looking at trying to use an led array that are all one chip, and perhaps slightly larger than the aperture diameter. These are available in various sizes and brightnesses, so something might work out. I have another idea too, that needs thinking through, though.
Posted by Bill Brandenstein (Member # 892) on October 01, 2013, 11:50 AM:
You will keep us posted as to your findings, I hope! Thanks, Jon.

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