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There are lots of potential issues with this, not the least of which is the difference in color spectrum between the two types of light sources.
 

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Issue 1: Bypassing the ballast UHP lamp power supply for the projector since the mainboard on most projectors won't even power up if the microcontroller doesn't detect a sustained arc (and light) from the UHP lamp.

Issue 2: Schematics aren't provided for most (computer projectors which I guess is what you're talking about) which would require some reverse engineering to achieve Issue 1 (time consuming).

Issue 3: High lumen output LEDs would be extremely expensive. Also high output LEDs need cooling for the dies just like UHPs do. If you've ever owned a high powered LED flashlight you'd see the heat the dies generate at only a few watts.

Issue 4: Hotspots you would probably have to use an array of LEDs to achieve enough light and without a proper reflector and lenses to bring the separate light sources into convergence with each other you would have sunspots all over the projected image brighter at the center and dimmer on the outside edges of the individual LEDs.

Issue 5: Light output temperature the projectors DLP color wheel or the diachronic color filters in an LCD projector are designed for the color temperature of a UHP lamp. A different temperature from the LEDs would cause colors to be off not to mention the temperature discrepancy of the separate LEDs in the array.

There are many other issues but these are the main hurdles I can think of off the top of my head. Suffice it to say this isn't a weekend project.

Optical trains are designed around the characteristics of the light source which is what makes this such a challenge.

I know UHP lamps are expensive but they are difficult to manufacture and most of them are still handmade by glass blowers and skilled craftsman so that adds into the cost. Not to mention the precision alignment equipment needed to position the arc tubes in the reflector properly.
 

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I wish it were true. But I think LED's, as nice as they are, are still far away from being economical options for home theaters for the masses.
 

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It would be nice for it to work and cut/reduce wattage and extended life of the light/bulb as replacing a bulb for most video projectors isn’t cheap. That’s why I use my widescreen Panasonic CRT mostly for regular viewing and the LCD video projector for new film DVD/Bluray usage.

So I shouldn’t be replacing my bulb till around late 2010 since I only brought early this year second-hand with new bulb that the owner installed before selling it.

I have seen an LED video projector at Maplin Electronics for £120.00 pounds not sure if the specification is high enough for average fair robust quality?
 

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what about using HID ?

they use less power and 6000k bulbs should be a nice white

would a HID survive an UHP's startup or would I have to bypass

yet to look into the voltages ect

my idea is drill into the old reflector housing and just sit the HID in that .. any other electronics needed could fit inside the PJ's casing still ( well in my case any how )

its only for my 3m x 3m bed room

its a old 720p PJ TX100 and do not plan on replacing its LAMP another time
( internal fans driving me crazy its not the LAMP fan it seems to be something else more internal so trying to cut back on the heat the PJ creates )
 

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I remember LUMENLAB, I was going to build a projector based on their design, but decided to buy a real one.

A mini CNC would be handy as well :)
 

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MasterCATZ - did you ever try to put an HID into your PJ housing? sounds like an interesting project...
sorry for not replying

bypass is this


http://img692.imageshack.us/img692/4561/yee5iy1tr6.jpg
PSU is this

http://ep.yimg.com/ca/I/yhst-52710754368872_2218_33387469
Guide is this

http://www.diyaudio.com/forums/diy-projectors/141537-commercial-projector-ballast-bypass-guide.html
The ballast was pretty easy to bypass after some poking around with a multimeter.

***For those of you that are having trouble bypassing the ballast on any projector***

1 - Find the group of wires that come from the ballast to the main board.
2 - Power the projector on with NO lamp.
3 - Measure the voltages on all the wires connecting to the main board.
4 - Find the wire that is close to +3V
5 - Insert lamp (If you have one) and power on. Measure the voltage of this wire again. The voltage should be around 0V
6 - Connect the spot on the board where that wire connected to a ground on the main board.

This will bypass the lamps for 90% of projectors. It has worked for me on about 8 different models. All else fails just ground each wire and power on and see if the projector stays on. Remember that the wires coming from the board need to be grounded NOT the wires coming from the ballast.

This seems to be a frequent question/problem. Maybe this can be made into a sticky since commercial modding is getting popular.
 
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