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Projector LED conversion

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Avalanche

Wed Aug 27 2008, 09:35PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

This is something that I'm hopefully going to be attempting over the next few weeks / months

I have aquired a rather nice Toshiba DLP projector that is fully working except the lamp is missing. I have no intention of replacing the lamp with an original part, but I have been toying with the idea of converting the projector to LED - maybe by using a 20 watt power LED (something proven like Cree). I'm prepared to accept that I will not be able to get full brightness, but I figured that if this thing is bright enough for a room full of people to view during daytime then even a fifth of that brightness will be more than enough for home... maybe.

The main purpose of this thread at the moment was to just stir up thoughts and ideas before I get too stuck into it, I'm guessing there are people here who know a lot more about projectors and optics than I do.

A few things I need to do will include building some kind of ratsnest to emulate a working (metal halide?) lamp, so that the projector does not complain. The second thing that is concerning me at the moment is the beam angle of the LEDs I have been looking at. They tend to be about 100 degrees, not sure if this is even worth mentioning! Clueless when it comes to optics. It looks like there is a small lens fitted inside the lamp compartment to 'pre focus' the light, however this is not part of the replaceable lamp module. Initial attempts at shining a 3 watt LED module into this window were very unsucessful - there was only a dim glow visible in the lens.

I'd be interested to hear other peoples thoughts, is this ever going to be possible, are there any 'gotchas' that I've missed, etc. I'll keep this thread up to date if/when the whole thing actually starts coming together

Steve Conner

Fri Aug 29 2008, 09:07PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

You'll come up against the fundamental problem that a projector arc lamp is much more intense than LEDs. It might only be 125W, but all of that power comes from a tiny spherical arc a few millimetres in diameter. Philips boasted an intensity of 1GCd/m^2 for their projector lamps.

This point source makes a highly focusable beam that the projector designer can turn into any shape and size he wants. It's so good that they are prepared to put up with the 40 bar pressure in the bulb and resulting violent end-of-life explosions. (OK, I admit the high pressure helps with colour rendering too)

LEDs are much more diffuse: look at the total chip area of a 125W LED. And there's no way that I know of to concentrate that postage-stamp sized glowing square back into an equivalent intensity to what the arc has. That's probably why your attempt with the LED failed. (or then again maybe it failed because the projector's DLP, LCD or other light modulator stays black until it's powered up.)

Avalanche

Sun Aug 31 2008, 01:45PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

you're totally right

can't get enough brightness

I'm now one foot in the sea of wtf with this project... I'm obviously going to be limited in LED choice by the size of the chip in the LED. The one I'm currently using (3 watt) has a chip approx. 3mm^2 and it doesn't look like I can go much above that in terms of physical size. I'd wrongly assumed that a projector just used a pretty normal metal halide lamp that shone through the LCD. wrong!

Anyway, I mounted the 3 watt properly, shining directly into the little light tunnel thing. I can get an image, but even with the lights turned off I can only just make it out on a piece of A4 paper held a couple of feet in front of the lens. I'll try and get a picture of that the next time I get all this stuff out again.

Because I've got this far, I'm going to try and buy a more powerful LED with a similar chip size and see what I can make it do, can't really lose now because even if it fails I'll have an absolutely ridiculous LED left over to play with

Seoul_lasers

Sun Aug 31 2008, 03:30PM

Registered Member #1630 Joined: Sat Aug 09 2008, 11:36AM
Location: Seoul Korea
Posts: 115

I have a rather interesting idea, You can use a 35W HID for a car?

Steve Conner

Mon Sept 01 2008, 12:10PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Why? Those things are expensive, you might as well spend the money on the proper replacement lamp and have something that's guaranteed to work.

They also have a longer arc than a projector lamp, so you'll have the same problem.

Look at this for an idea of what projectors are designed around:

Conundrum

Fri Sept 26 2008, 10:28PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

use one of those ceiling mount spiral "flat" CCFL fluorescents? those are pretty bright for their size.

-A

Staci

Sat Oct 04 2008, 03:42AM

Registered Member #1741 Joined: Sat Oct 04 2008, 02:45AM
Location: Schenectady, NY
Posts: 35

Eek - this happened to me a while ago =( - I used to design these projectors, but took a better real job with real company and can't steal lamps anymore.

LED can be bright enough - but it takes some doing. P-VIP lamps (mercury halogen) usually are 4x the projector rating in lumens. My IBM C400 DLP uses a 250W P-VIP lamp at 10800 lumens , and the projector yields 2650 (new lamp, 65F ambient).

car HID headlamps won't work - because they're AC - and beat with the color wheel refresh. The reason the projector lamps are so 'spensive - is because they're DC , and there's a current loop to boost red and de-emphasise blue (those lamps have uber ridiculous cyan and yellow lines). Osram trademarks this as Unishape. Yay for silly names that mean nothing. Arc is very short, and usually in an elliptical reflector, elliptical moves point source of light from one foci to the other. Foci 1 is arc, and foci 2 is at the color wheel immediate before light integrator quartz rod.

20W LED white multi-dice worked dissappointing, even with 3 of them (3000 white lumens), and combining optics and diffuser was expensive to make.

I eventually went with photonic lattice LED, from

- that has uniform surface emitter, and measure 490 Ansi lumens, and have closer to D65 balanced white output. You can get 4:3 lattice LED but they are getting rare, as the world moves to 16:9 .

This ancient history now, but Good luck!

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