Overhead Projector, an LED upgrade?

Joe Smith

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Feb 15, 2009
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In our classroom we make frequent use of an overhead projector. While we have the funds for a shiny new model I have repeatedly declined the offer in favor of a vintage model that is much heavier duty. However, being old and crickety the light output is rather low and it gets hotter and smellier than I would like. I've overhauled the rest of the machine and painted it flat black (until I can put flames on it) but the workings are still from the 70's.

(An example of my model)
beseler.jpg



I was wondering how difficult it would be to replace the bulb with a group of powerful LED's? I need it to be powered by 110v and while I can do a LOT of fabrication work myself but am not too handy with soldering and get WAY over my head with LED's, Drivers, Power sources, ext... (everything needed to do this project basically) so if there is a unit ready made for easy drop-in that would be helpful.

What are my options?




The heart of the beast:
beamer_gehause_s.jpg
 
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Here is a link to the LEDs being use in several new small portable projectors. I'm unsure what is needed?

http://www.luminus.com/content1092

I don't have any first hand knowledge or any hands-on work with these, or the companies other LED engines.

If memory serves me correct, they are getting 2,750 lm with a drive current of 13.5 Amps, with one white module I was looking at. I don't have the specs in front of me, but I remember them having a good thermal design to handle such high drive currents.

Does anyone have any first hand use of these. I also have no idea of their cost. I mention them, having seen several press clippings about them in projection systems.

I don't know what the output of the bulbs used in those overhead projectors, but I've seen others using a Metal Halide lamp, and a flat screen to create a projection TV system. How much light does it take to use one of these . . . or . . . what is needed to replace the stock bulbs with LEDs?

Anyone here have any experience with any setup like that?

It's late, but I think I got my info correct. If not, please feel free to correct or comment. :tired:

Good Luck . . .
 

HarryN

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I have not seen one of those in a while - but it makes for an interesting project. Probably not too hard these days with plenty of options.

Normal light bulbs are "voltage based" which is the reason for that transformer. LEDs are "current based" which means you need a replacement for it.

I suggest to use the 110V based "xitanium" drivers. The quality is high and the price is reasonable. One (of many) companies that sell them is ledsupply.com - here is a link to their xitanium page. http://ledsupply.com/xitanium.php Since it is a bit difficult to really know how much power will be needed, it might be useful to consider a version with a dimmer.

The next step is to decide "how much" LED lighting power you will need to run that projector. A very good estimate is "about the same as you have now" in that light bulb. I am going to guess that it is around 100 - 200 watts - really - completely a guess - just look at the bulb and it should say on it.

The inside of that projector is acting like a giant "light box and light output smoother". It isn't very efficient, but it works. If the light from the LEDs were really being directed "upward" with some very floody type reflectors, the energy demand might drop to 25% or less. An example of a floody reflector is one that is very rough on the inside - almost sanded like qualities.
 
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HarryN

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The next part of your decision relates to the LEDs themselves, but also - how you are actually using the projector.

White LEDs can be optimized for high color content or brightness, but not both. If the projector is being used mostly to project ink to the wall (black, blue, red, yellow) then you can use an LED with a higher color temperature (5-6,000 K), more output per watt, and less color content.

If instead you wish to use it for photographs or to project through an LCD screen, then you will probably want to use LEDs that are a bit warmer toned - perhaps a 4000 - 4100 K temperature. I am guessing that this is close to what you have now.

There are some even higher color content LEDs, but I don't really think that it matters and they have relatively low output.
 

HarryN

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The decision on the exact LED and LED brand itself gets into personal opinion. I think most people here would be comfortable to recommned either Cree or Lumileds as brands, and both make very good quality parts that will work. There are other good LED options out there as well.

If color quality is not a big concern, I suggest that you stay with an LED package with
- a single die per package
- About 5 watts capable each
- About 500ma - 1,000 ma capable each
- cool white
- Already mounted onto a "star" PCB mount ( sort of an industry standard, easy to use mount method)

This will make the mounting and installation easier.

One of the reasons to go with "multiple, lower powered LEDs" instead of "one big one" are the particular optics of that setup. The table acts like both a ground glass and fresnel lens, focusing the light down to the head. The design sort of assumes that the light is appearing to come from the underside evenly and from a long distance (infinite focus). At least I think this is the concept. Perhaps it would be good to "test" this assumption by placing a few MR16 size lamps in there and see what happens.

Here are a few examples:

The Lumileds K2 and K2 TFFC (web page) http://www.philipslumileds.com/products/luxeon/luxeonK2

The ledsupply.com web page http://ledsupply.com/

Cree's web page http://www.cree.com/products/xlamp7090_xre.asp

You can spend a very large amount of time finding the "optimum" solution for power vs cost, etc, and then will find out you are experimenting just like all of us. That is 1/2 of the fun. I know more about the Lumileds products for historical reasons, and others know more about the Cree products or other brands. Frankly, any of them can be "made" to work.
 
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HarryN

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The LEDs will need to be mounted on a heat spreader with a fan to cool it. Try to find some kind of setup with fins such as one with fins.

Perhaps someone else will jump in with some ideas. Sorry for using several posts to answer, sometimes it is better to break these up so there are not lockups.
 

HarryN

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If color quality does turn out to be a bigger deal, one option to consider is this RGB setup, which can "fool" your eyes into thinking they are seeing high quality white.

http://ledsupply.com/07007-rgb-01-3.php

Color mixing to make "white like" light from RGB can be a bit tricky. It is not that hard, but perhaps consider to hold off on this approach until you do "version 2". :grin2:
 

FGS

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Hello

What brand it is and model no.? What sort of lamps goes in there? (ANSI code, wattage, and voltage.)

Thanks.
 

65535

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I believe that the top plate in the projector is a fresnel lense. There is no practical way to use leds as they can not all be put within an acceptable focal range. You would be better off looking for a properly specked HID lamp and ballast. Normally those overheads run around 350-1000 watts, most school ones and probably yours being around 350 watts, so I would imagine you would be looking at a 100-150 watt HID lamp with a smiliar sized arc tube to the original filament.
 

HarryN

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You are probably right that it is a fesnel, but what I am wondering about is the initial distribution of the light already there in the box.

It appears that the top of the bulb is "coated" to force all light emission to come from the long sides. If this is the case, then more or less the deep box is acting like a smoothing integrating sphere. If this is little more than random, smooth light coming from the bottom and sides, then this can be relatively easily dealt with using LEDs and sanded reflectors. It might be that the energy efficiency can improve a factor of 10 with some light management.
 

65535

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Actually, you're probably right, the fresnel collects the light and the focal point is actually at the adjustable lense assembly in the top. So having a solid plate with LED's evenly distributed with no reflectors on the bottom would probably work. But the power might be up there.
 

FGS

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You might try one from Maxlight Tech. Not sure if they're any good or cheap. I think the LED has 100 1w LED diodes inside from what I can see on the tiny pic.

I am new in LED lighting so I don't know much about them.
 

kineticm

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Jul 7, 2021
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Sorry to bump an old thread!

I'm looking to do this (exactly twelve years later).

What kind of kit could I buy on today's market it replace an overhead projector lamp with LED(S)?

Would the result be more or less bright than incandescent?
 

LEDphile

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While I'm not sure if any kits are available, retrofitting an overhead projector with a CoB LED should be a straightforward exercise. You'll need to replace the transformer in the projector with an LED driver (readily available from a number of vendors), and replace the lamp module with a CoB module and suitable heat sink. If possible, you'll want to keep the fan operational. With the larger CoB modules, you should be able to get as much light out of the projector as with the original lamp, although you will probably need to play with the distance from the CoB to the stage glass to get a good balance between even illumination and efficient use of the light (as the CoB will have a wider beam than the old reflector lamp assembly).
 

bttags

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While I'm not sure if any kits are available, retrofitting an overhead projector with a CoB LED should be a straightforward exercise. You'll need to replace the transformer in the projector with an LED driver (readily available from a number of vendors), and replace the lamp module with a CoB module and suitable heat sink. If possible, you'll want to keep the fan operational. With the larger CoB modules, you should be able to get as much light out of the projector as with the original lamp, although you will probably need to play with the distance from the CoB to the stage glass to get a good balance between even illumination and efficient use of the light (as the CoB will have a wider beam than the old reflector lamp assembly).
Any solutions yet? Without any experience, I am trying to find a light / LED upgrade so that the machine doesn't get so warm, so quickly. I'm using an Elmo brand overhead projector.
 
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