# Suggestions on how to replace projector bulb with an LED



## guyburns (May 28, 2017)

*Background*
I have 10,500 ft (7 hours) of old 9.5mm film to go through. I'd like a proper viewer, but they're extremely rare in Australia. A film viewer is like a slide viewer Â– uses a low wattage bulb to show a small image. Instead of a viewer, I want to:


use a 9.5 mm projector
replace the 100W lamp with a bright LED and lens
throw a 200mm image on a sheet of paper
and step through the films at the slowest speed.
 
I have experimented with a Zebralight head torch (see http://www.mediafire.com/view/aq6apypayq0a0cd/Projector_02.jpg). Amazingly, I can get it to fit in the existing setup without modification. It just slides in. Three problems: the torch is a 90º beam type; I would have to keep changing batteries; and the image is a bit dim.


*My Idea
*My idea is to use:


A high power LED, probably something from the Cree XML-2 range.
A ready-made power supply, preferably driven from 240 volts or 12 volts AC. Variable current if possible, over the full range of the LED. But fixed current is also okay.
A 10º lens.
The size of the original focus device is 40mm diameter. The whole lot must easily fit into a space about 50 x 50 x 50 (see http://www.mediafire.com/view/fu47qa9tjqa1afu/Projector_01.jpg)

*Ques 1
*What type of LED, power supply, and lens, would be most suitable? I'm not concerned about colour temperature. I simply want to view, edit, and send away for scanning.

*Ques 2*
How many lumens would I need to throw a 200mm image with an equivalent brightness to the original bulb? The bulb is 100W and the instructions say not to exceed an image 5 feet wide. I assume the manufacturers consider an image larger than that to be too dim when using a 100W bulb.

*Ques 3*
What would be a suitable beam angle for the lens?

*Ques 4*
Are there any household-style 240 LED lamps that might be useable? One that has a narrow beam, for instance. I'm thinking of pulling one apart and experimenting.


Thanks in advance for any suggestions.


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## HarryN (May 29, 2017)

It is a bit tricky, but possible. 

First, the challenges that need to be thought through as you consider an LED based equivalence:

In the US, the 100 watt bulbs used for projection are roughly:
- 1 000 lumens
- 5000 K CCT
- Quite high spectral quality
- Very high surface brightness (often by using clear glass instead of frosted and quite compact filaments)

Usually this is combined with 2 stage optics which are quite effective at capturing the bulb output and directing it. They are a true "focusing optics" vs most LED optics are "non focusing" optics.

It is rare to find those combinations in a flashlight type head because of the size and complexity. It can be done, just a bit more challenging.

LEDs aspects:
- CCT isn't a big problem
- High surface brightness - that is more challenging for LED
- High spectral quality - achieving this and high surface brightness is even more challenging
- 1 000 lumens - it is a lot of light, but possible
- Multi stage optics - might have to be creative


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## HarryN (May 29, 2017)

I spent quite a bit of time, partially because I had no idea what I was doing, playing with single stage and two stage optics to achieve a good projection type beam from a fairly large LED beam. Usually what ends up happening is that only a surprisingly low % of the beam ends up having the correct optical properties and you end up throwing away the rest.

Perhaps consider to start with a 2 - 3 K lumen, high throw light of some kind, tunnel the beam into the projector and run a power supply to the light. There are some hand held search lights like this.


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## guyburns (May 31, 2017)

Thanks for the responses.

I wasn't really thinking of using an LED torch, but a stand alone LED with a focussing lens and a driver

• Colour temperature or CRI is not important as this is for editing (and subsequent scanning) of B&W films.
• High power is not important. Most editors use a 10 Watt bulb.
• Smoothness of light across the image is not all that important either.

Basically, I want a simple-to-implement LED system that throws an A4-size image for temporary use while editing.

Any suggestions as to components, particularly the power supply, and where they can be had from, would be most appreciated.


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## FRITZHID (Jun 1, 2017)

XM-L2 on a 50-100 watt copper core heatsink and a simple driver will do the lumens part just fine. i've even ran them directly off a 5v 2a cell phone charger with no driver/ballast and they work well, but be aware, this configuration can be a tad hard on those little cell chargers and they can/do burn out but seeing as i have 10s if not 100s of them lying around, i can spare a few. 
as far as lensing goes, use a piece of fine sand paper to scuff the dome of the LED (will blend in the die lines better for lensing) and then the stock 2 projector lenses that came with your projector should work just fine, i tinkered with an old slide projector and this setup worked very well for images up to about 3ft sq. there was some lens apparition around the outside edge but that bothered me none. just try to get the LED in the same location as the stock filament was.


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## lf-mark (Jun 7, 2017)

Perhaps it'd be easier to build something like the viewer with a smooth white evenly-luminous surface past which the film is run, then use a camera trained on the film (rather than on a projection) and monitor to do the enlargement. Fewer heat issues and easier to construct.


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