replacing a projector bulb with leds

[Simon]

I was recently given a projector. I decide to find out how much a bulb replacement will cost. err: nearly the price of a newer and better projector.

But can a projector bulb be replaced with leds ?there is plenty of room. My only worry is that I can't use the 380V supply to the old bulb and if the projector finds that the bulb is missing t will fail to work

[joelby]

Yes, it seems like a number of people have done it before:

There's usually a control signal that indicates that the bulb is present.

[mikeselectricstuff]

Although you can do it, brightness will be a tiny fraction of what it was with  the bulb.
I believe there are some cheap third-party replacements for some bulbs so worth lookking around.
 

[johnwa]

Hi Simon,

There is a lot of info on DIY video projectors over at http://www.diyaudio.com. I think some people over there may have done what you are proposing.

[mikeselectricstuff]

Many (most/all?) projectors use an Osram ballast, and there are a couple of standard control/monitoring protocols documented on the Osram site, so faking the ballast to trick the projector into working should be doable.
Some links to protocol documents here

Might also be worth investigating automotive HID headlamp bulbs - aftermarket lamp+ballast kits are pretty cheap on ebay

[Simon]

well having looked at it all I can see is a switch to tell it that the lid in on the bulb compartment. Could there be feedback from the bulb driver ? At the moment is looks like I just need to setup the leds and find a way of powering the leds (presumably not from a 380V ballast supply  )

Is there any chance of buying and old bulb assembly that I can work on as that is the easiest way of getting the leds to fit in but I'm not canabalizing the good bulb I do have

[Fraser]

Simon,

I went through the same process that you are about to embark upon....making an LCD/DLP projector work with a cheaper light source than the OEM lamp.

I soon discovered that the OEM lamps are pretty sophisticated components. As an arc lamp they are ignited by the Ballast module and the current carefully monitored by Ballast management circuits. Once the management circuits are satisfied that the lamp has lit and the arc is stable, they will send the required 'lamp ok' signal to the main board. Normal hacks to fool the main board are to intercept the control line from the ballast to the main board but exact details vary from brand to brand.

The Lumen output of a projector arc lamp is quite amazing and is needed to overcome the inherant losses in the optical block and associated LCD panels. DLP is more efficient in this respect as LCD panel attenuation is removed from the equation. It must also be understood that the arc lamp is a point source of intense light and the lamp refector very accurately projects that point source of light onto the projectors light guide assembly 'sweet spot' any error in this exact concentration of light in the right place causes large losses of efficiency. You will appreciate that using many LED's spread over a large area to illuminate the light guide will be inefficient unless optics are used to focus the light to the correct point. Not an easy task. The use of a single how powered LED is a possibilty but there is still a need to focus the emitted light on the correct area of the light guide and the lumen output of a single LED is pretty pitiful when compared to an arc lamp. An LED solution usually relies upon the viewer sitting in a virtually blacked out room which isn't that convenient in many cases.

I investigated high power LED modules and all manner of halogen light sources. All were proven to be unsuitable or too dim for the task of making a decent projected image. Remember the colour temperature of the light source is very important for a decent image. It is possible to build an LED replacement for an OEM arc lamp but I would consider it more of a hobby challenge for the fun of it, rather than trying to produce a usable projector.

There are some other options available to you:

1. Hunt on ebay for the right lamp at a good price ... they do appear occasionally.
2. Find out about the arc lamp technologies and buy a suitable cheap donor lamp module for an unpopular model projector that uses the same burner and fit that in yours (I have done this with excellent results)
3. Buy a new burner (the arc bulb) for around $60 from China and fit it in a cheap burned out OEM lamp module from ebay.
4. Buy a complete burner/reflector assemply for around  $120 from China and fit it in a cheap burned out OEM lamp module from ebay.
5. Forget relamping the unit  and just buy a few cheap used projectors on ebay in the hope that they have good lamps (I have done that very successfully)
6. Buy cheap faulty projectors on ebay and hope the lamp is OK and the fault is simple to fix (I have done this 11 times and fixed all of them but only 8 had decent low lamp hours on them)

My greatest buy was a Panasonic projector that had been dropped but suffered no external damage. When inspected, I found a filter torroid had pulled one of it's leads out of the PCB..... 2 minutes later I had a working 'as new' Panasonic ultra portable projector. It cost me £30 total inc delivery and had only 250 hours run time on the chassis and lamp. Thankfully it was dropped onto a softish surface and the unit was off (lamp cold) combined with a probable dry joint on the torroid....life was good that day.

If you do decide to buy used units, faulty ones are often a better buy (if you can fix them) than ex education units as those have horrendous hours on the chassis, are often not cleaned regularly and have worn out lamps that are good as dead. A faulty unit hopefully fails whilst there are plenty of hours left on the lamp and the chassis is relatively young.

A free projector can be more hassle than it's worth !.... if it has high hours on the chassis, and is LCD, it likely has cooked LCD filters as well so really isn't worth the bother to get it going. There is a very good reason why a retired LCD projector that had a RRP of say GBP1,600 sells for just GBP20 on ebay when the lamp dies. The chassis ages as well as the lamp.... filters and LCDs degrade and basically they are spare parts donors.

[Simon]

Well in "that light" I'll probably run it till it breaks and then either buy another one or get a new OEM lamp. My intention was to use it mostly for Rotaract events so if i charge a fiva a go for projector use hopefully it will pay for a new projector or lamp.

[Fraser]

Simon,

It would be worthwhile and I think interesting for you to do some googling on metal halide projector lamp theory and technologies. This is what I did and I discovered some very interesting facts regarding the different types of burner and importance of using the correct wattage burner for a particular Ballast. Interestingly, in the case of arc lamps, if you use too low a wattage burner, it dies quickly and if you use too high a wattage burner it also dies quickly ! It's all to do with correct electrode temperatures and arc gaps. It's actually quite an interesting subject and you will realise why projector lamps are normally so expensive. They are precision manufacured components using some very clever technology and exotic materials in their manufacture in order to maintain long life and correct colour temperature.

You will discover that there are several different patented burner technologies, some are AC whilst others are DC driven and the electrodes can be blunt or pointed. Some have a spiral ignitor wire whilst others have a tight noose around their necks ! All good fun  

I used to buy all manner of cheap projector lamps on ebay. They were cheap because they were designed to fit unpopular projectors. The important part was the burner though. Many projectors share the same burner specifications so it is a case of doing a transplant into your OEM lamp module. Not a task for the faint hearted as it involves removing the burner from it's reflector and installing it into the reflector of your module using ceramic mortar. Precision placement is required otherwise the burner cooks itself and light output is defocussed ! If you are really lucky another projector uses a burner/reflector combination that is identical to your projector but life is often less convenient !

You should never run a lower power lamp in a projector and using a higher power lamp will possibly work if the Ballast can produce enough voltage to strike the arc across the increased gap size, but the burner will quickly suffer metal splattering on it's internal surfaces due to low electrode temperature and failure will follow. With regard to failure of a projector lamp.... There is a very good reason why the lamp module is effectively armoured .....the burner is very thick walled to containg a very high pressure halide gas mixture. If the glass envelope breaks, expect a loud BANG ! and lots of shards of glass to fly in all directions within the module. Containment is usually good though. Other less dramatic failure modes are melting of the glass envelope with slow pressure release, electrode wear exceeding the capability of the Ballast start voltage so no arc occurs and the ballst shuts down and finally clouding of the burner due to metal cast off from the electrode (old age). The explosive failure is the most dramatic and the reason why projector manufacturers are at great pains to inform the user of the Lamp modules predicted maximum run time. They are trying to stop the use of the lamp before the burner suffers catastrophic failure which is quite common if the maximum hours are exceeded significantly.  Many projector manufacturers force the user to stop using the lamp module at a preset number of runtime hours by placing a warning on the screen and after another period of time the projector will start, display a warning and then shut down to prevent burner failure. Many users reset the hours meter to gain more life out of the lamp module but this usually risks lower light output from the burner, intermittant start, colour temperature impurity, flickering and possible explosion of the burner. Saying that, I have a Panasonic projector fitted with a 2000h lamp that has now exceeded 2700 hours and is still going strong ! If you take care of projector lamps and let them cool properly before moving and do not use them regularly for very short periods of time they tend to exceed their predicted life. Also it is a good idea to run the fans in their 'normal' or high speed (high altitude) mode and at reduced output as this significantly lengthens their life. So called quiet or wisper modes with reduced fan speed and hence cooling do the burner no favours at all.

You have not told us what projector you have. Some of the cheaper projectors use very cheap metal halid burners without a reflector as that is part of the projector chassis. These burners have a shorter life, less accurate colour temperature and look much like the 500W halogen tubes or cartridges used in security lights. They have the burner bubble on the middle of the armoured outer tube. Such burners cost only around £25 but they cannot be transplanted into the higher performance projector lamp modules as the arc gap is huge ! These types of Metal Halide lamps are really designed for security light fittings but those clever Far East manufacturers have found another use for them

Useful web pages:

http://en.wikipedia.org/wiki/Metal-halide_lamp

http://en.wikipedia.org/wiki/UHP_(lamp)

http://www.projectorlampexperts.co.uk/LampAdvice-TheScience.aspx

http://www.lumenarc.co.uk/forum/showthread.php?249-How-to-replace-a-Projector-Burner

[Psi]

Just looking at some figures from wikipedia....

Metal halide is 65-115 lumens per watt
A good LED (ignoring the efficiency losses in the powersupply) can be up to 150 lumens per watt (and i'm sure i've seen CREE saying they have leds over 200L/w now).


Deal extreme sell a 100W led array which supposedly puts out 8000lumen so 80L/W
http://www.dealextreme.com/p/prime-100w-8000lm-led-emitter-metal-plate-pure-white-42806

That's probably what i'd try first if i was doing a conversion, probably only get 50% of the original projector brightness but being a single module it would be easy to try.

[Zero999]

Just looking at some figures from wikipedia....

Metal halide is 65-115 lumens per watt
A good LED (ignoring the efficiency losses in the powersupply) can be up to 150 lumens per watt (and i'm sure i've seen CREE saying they have leds over 200L/w now).

Take that information with a pinch of salt, as you said, it doesn't include the power supply or the luminaire so the actual efficiency is less, for example 22% efficiency is sited for the best raw LED, but the best figure given for an LED with a 120V power supply is 13.6%.
http://en.wikipedia.org/wiki/Lighting_efficiency#Examples_2

[Hideki]

Take into consideration that many HID projector lamps are in the 200-400W range, which is hard to match with a single LED, even if it's more efficient.

As an example, take one of the most powerful single-LED flashlights available:
http://www.amazon.com/Olight-SR90-Intimidator-Luminus-Flashlight/dp/B003CT5GOG

2200 lumens / 30W = 73.3 lumens per watt. That's similar to the number quoted for metal halide.

So maybe you need ten such LEDs to match the output?

[mikeselectricstuff]

Just looking at some figures from wikipedia....

Metal halide is 65-115 lumens per watt
A good LED (ignoring the efficiency losses in the powersupply) can be up to 150 lumens per watt (and i'm sure i've seen CREE saying they have leds over 200L/w now).


Deal extreme sell a 100W led array which supposedly puts out 8000lumen so 80L/W
http://www.dealextreme.com/p/prime-100w-8000lm-led-emitter-metal-plate-pure-white-42806

That's probably what i'd try first if i was doing a conversion, probably only get 50% of the original projector brightness but being a single module it would be easy to try.

The problem with power LEDs like this is that the source is spread over too wide an area to be able to focus down small enough to get any significant proportion of the light in to the optics system.

[Psi]

surely you could just mounted it a little further back and/or put a lens over it?

Actually, don't projectors have a focusing lens around 50cm diameter already, so they would expect light over a pretty large area?

[mikeselectricstuff]

surely you could just mounted it a little further back and/or put a lens over it?

Actually, don't projectors have a focusing lens around 50cm diameter already, so they would expect light over a pretty large area?

No, because it needs to focus onto the DLP or LCOS modulator, and you can't focus a large -area source down to a small area. The benefit of a discharge lamps is they produce their light in a very small area.

If this was possible don't you think manufacturers would all be doing it this way instead of using expensive and exotic discharge lamps? here area few LED projectors but their brightness is a small fraction of that from lamp based ones.

[tecman]

I have a 50" Samsung DLP with LED illumination.  They use:  http://www.luminus.com/products/white.html

The attached link is for white, but the Samsung uses red, green and blue LEDs but in your case you would need a white device, so that is what I linked.  As you can see, they are very high power and will require some cooling as well.

Paul

[mikeselectricstuff]

I have a 50" Samsung DLP with LED illumination.  They use:  http://www.luminus.com/products/white.html

The attached link is for white, but the Samsung uses red, green and blue LEDs but in your case you would need a white device, so that is what I linked.  As you can see, they are very high power and will require some cooling as well.

Paul

With RGB LEDs, they can 'overlay' the LED die images with dichroic optics to get a smaller effective source, and each LED only runs at 1/3 (approx, depending on adjustments for relative output) duty, so they can be cooled more easily as the heat is spread over 3 devices which can be spaced out a bit.
White LEDs have inherently bigger effective area due to the phospor. RGB LEDs are also a lot more efficient - a white LED solution would be throwing a lot of the light away in the RGB filter of a projector designed for a lamp, wheareas almost all the power of the individual R,G,B LEDs will get used. 

[Simon]

there is a 15m square window (lens) for the light to go through I thought this was ideal for a led to point at.

The model is an optoma DS302 takes a 180W lamp that costs £100

[Fraser]

Simon,

I know the model well, I have two from that Optoma series.

I found the lamp module here for GBP75, presumably plus VAT & postage.....

http://www.everythingforav.co.uk/projectors-lamps/projector-lamps/lamp-module-for-optoma-ds302-ep706-709-dx602-projectors.html

Believe it or not the lamps for that projector are bargain priced compared to those for other makes ! GBP 200 - 300 is not unusual for a lamp. The lamps for these projectors also appear quite often on ebay at pretty good prices. I paid just GBP14 for a new one.

Building an LED lamp assembly, even if it worked would not be a cheap exercise either.

To note regarding the DS302....

The unit is a DLP projector using quite a basic design of colour wheel and so can produce noticeable rainbow and colour strobe effects for some viewers especially if not viewed directly.

Watch out for the front adjustable support leg ....if banged of dropped, the spring is ejected from the foot shaft and into the internals of the projector where it usually ends up in the PSU, killing it    I have repaired several with such a fault.

[Simon]

Thanks Aurora all helpful advice

[Zero999]

With RGB LEDs, they can 'overlay' the LED die images with dichroic optics to get a smaller effective source, and each LED only runs at 1/3 (approx, depending on adjustments for relative output) duty, so they can be cooled more easily as the heat is spread over 3 devices which can be spaced out a bit.

I also wouldn't be surprised if they do clever things like reducing the brightness of colours which don't feature much in the image to save power, for example if a scene hardly has any blue, they could dim the blue LED slightly.

Another possible advantage is they could potentially achieve a higher resolution by using a monochrome display but multiplexing the colours, so the red, green and blue elements are displayed sequentially at such a high frequency they blend together.

[Simon]

No if you dimmed one colour it would affect the rest - trust me I've worked in printing. not sure about high speed swapping of colours, might take more intricate faster electronics than is worth it

[mikeselectricstuff]

With RGB LEDs, they can 'overlay' the LED die images with dichroic optics to get a smaller effective source, and each LED only runs at 1/3 (approx, depending on adjustments for relative output) duty, so they can be cooled more easily as the heat is spread over 3 devices which can be spaced out a bit.

I also wouldn't be surprised if they do clever things like reducing the brightness of colours which don't feature much in the image to save power, for example if a scene hardly has any blue, they could dim the blue LED slightly.

I doubt this would be worth the effort - any savings would be minor, and matching the LED intensity scale to that of the modulator (LCD or DLP) would be a nightmare.
It would be probably worth controlling the relative on-time of each colour to get a neutral balance, although with DLP this would be complicated by the need to sync with the DLP's frame timing.

Another possible advantage is they could potentially achieve a higher resolution by using a monochrome display but multiplexing the colours, so the red, green and blue elements are displayed sequentially at such a high frequency they blend together.

DLP projectors (apart from very high-end cinema types which have 3 DLPs) have a monchome DLP and are switched sequentially, usually with a colour wheel. The actual modulation by the DLP is done by fast pulse-width modulation, as the micromirror positions are effectively either on or off. 

[torch]

I did the LED replacement thing in a slightly different application -- relamping an old optical comparator for which the bulb was discontinued. (an optical comparator is used in machining to project a magnified image of the part in question on a screen using reflected light.) In this case, I needed a very bright (~50,000 foot-candle) tightly focussed (80mm²) single-point light source with very even light distribution across the focal point of the projected beam. Grid array LEDs would not work -- while the light might appear even to the naked (and overwhelmed!) eye, the grid pattern quickly becomes apparent when magnified and projected.

I ended up using a Luminous Devices SST/R-90. The 90 refers to the maximum current of 9 amps at 100% duty cycle. Very bright. Can be used for street lighting. I am driving it with a commercial buck driver (the H6Flex by http://www.taskled.com) at 6 amps, but someone who knows more than I about designing and building these things should be able to make their own driver.

One thing that was a bit of a surprise for me, personally: I always thought of LEDs as being a cool light source -- not meaning the colour temperature, but rather the operating temperature. However, these high-power LEDs kick out a lot of heat just and are easily burnt out just like a CPU if you do not dissipate it. Mine is soldered to a copper disk mounted to a copper bracket with heat-sink grease and THAT is mounted in a heavy cast aluminium shell and I still need a cooling fan. (One nice thing about the H6Flex -- it has a thermal sensor and can be programmed to degrade the current as the heat increases. I set mine to a conservative 50°C)

So, very bright single source white LED emitters are available out there (and in a variety of colour temperatures too). A good resource in this area is http://www.candlepowerforums.com. Those flashlight guys are up on all the latest offerings and are making things that are so intense they could be classed as weapons!

[Zero999]

DLP projectors (apart from very high-end cinema types which have 3 DLPs) have a monchome DLP and are switched sequentially, usually with a colour wheel. The actual modulation by the DLP is done by fast pulse-width modulation, as the micromirror positions are effectively either on or off. 

In that case using an RGB LED will automatically incr4ease the efficiency by a factor of three and the LEDs can be derated as the duty cycle is 33.33%.