Advice/Help selecting LED for 8mm projector

[Brad Freese]

My goal is to be able to project 8mm home movies against a wall one frame at a time for a high quality image capture. I have an old Bell & Howell projector, but those bulbs run super hot and you risk damaging the film if leave the film in the gate for too long.

My solution is to replace the bulb with an LED. Typical projectors are around 1,000 - 1,200 lumens.

Does anyone have experience with super bright LEDs and/or can recommend where to get them? I'm having trouble figuring out the lumens for various LEDs. For instance, I'm looking at this model (http://www.ledsupply.com/leds/cree-xlamp-xp-l-high-density-led-star) in a single 1 up, Neutral White configuration - max light output is listed as 1226 lumens @ 10 W, but the in the Technical Documentation it's listed as only 478 lumens at 1.05 amps, 25°C. 

I'm also having trouble figuring out if super bright LEDs run hot at all, I realize the regular LEDs don't, but wasn't sure about bright ones.

Suggestions/Ideas?

[David Champion]

If you can get a LED with a big heat sink on the back, it may help keep the heat away from the film.

BTW, have you seen this project?

http://www.instructables.com/id/Kinograph-v01-DIY-Film-Scanner/

-dc

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[beernutz]

I know that some of the early LED lightbulbs had big honking heat syncs, but I think that was for the electronics that stepped down the voltage.  I might be wrong about the reason for the heat syncs, but I don't thing the LED's themselves put out appreciable heat.

[Ray Scheufler]

Bright LEDs need heat sinking that 10W of power usage goes somewhere.  I can bring the led and heat sink assembly from a CREE flood bulb down to the space if anyone would like to look at it.

The LED you linked comes on an aluminum backed PCB for a reason, it has pretty good heat spreading and dissipation.  I don't know if it will be enough for your needs.  If you are at the space some time I can help you read the datasheet and actually understant most of what it is saying.

Ray Scheufler

[Benjamin Miller]

By comparison, a modern desktop processor uses about 35 watts.  Think of how large the cooling is on the processor and consider what a 10 watt LED would require.

- Benjamin Miller <b...@benjamintmiller.com>
________________________________________
A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away.
    - Antoine de Saint-Exup'ery, In Design

[Nabil Hanke]

If your goal is scanning old video film, is this method the best? It would it be better to run it through a flatbed scanner? Set up an indexing mechanism and auto-crop. 

Also, not only is brightness very important but you should consider the spectrum the light source is emitting. Most leds are narrower than incandescent projector bulbs would be. You can probably do post-processing, but it would suck to have a band just missing. 

Thank you,

Nabíl

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[Matt Stanton]

This is only anecdotal, but I recently bought a 2000lm flashlight, and it throws a decent amount of heat radiated with the light at full power.  It isn't a searing heat like those projector incandescents, but it is probably uncomfortably hot within an inch of the LED.  I warmed my nose a bit with it last night, actually.

There are "warm white" LEDs that are designed to mimic the color of incandescent lights.  They are generally not as powerful as their soft and cool white counterparts, but it is easier (for me, at least) to "see" things I'm searching for when using them over soft white.  For some reason everything in the light field just looks the same as everything else in soft white LED light, while warm white light allows me to better discern color differences between objects being illuminated by it.  My assumption is that warm white light contains a wider range of color spectrum, or at least a range of colors that the human eye needs to bring out more color information (maybe the warmer spectrum highlights colors that are harder for the eye to see, while still providing enough spectrum to illuminate the blues and greens the eye is naturally able to see easier?).

Anyway, if the original projector and film were designed to use an incandescent bulb, a warm white LED may be a better choice.  You may just need to set the white balance of your camera for incandescent light to get the right colors.

-- Matt (N0BOX)

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