There are a variety of reasons. The most compelling economic reason is that you can build a pretty good high resolution projector for less than the purchase price of a new one with similar resolution, as long as your design falls in "the sweet spot": 15" LCD, two fresnels, a 400 W MH lamp & ballast, a fan or two, and an opaque projector lens. That combo will give you a 1024 by 768 projector that yields a very nice 95" picture, that can be driven by any source that provides a VGA-compatible output. For around $50 more you can add a converter box that will connect to S-video, composite, and component video.
The other very compelling economic reason is the cost of operation. The UHI-S400DD MH lamp I use runs for 20000 hours and then cost $44.52 to replace. That is many many times as long as a normal projector lamp, and 1/5th to 1/10th the price. When you go to buy a replacement lamp for your commercial off-the-shelf projector, you will discover that the lamp costs almost as much as your projector! And then you get to buy another lamp a few thousand hours later, and then another one a few thousand hours after that...
But of course, the main reason is the same for everybody on DIY Audio.com: fun!
The other very compelling economic reason is the cost of operation. The UHI-S400DD MH lamp I use runs for 20000 hours and then cost $44.52 to replace. That is many many times as long as a normal projector lamp, and 1/5th to 1/10th the price. When you go to buy a replacement lamp for your commercial off-the-shelf projector, you will discover that the lamp costs almost as much as your projector! And then you get to buy another lamp a few thousand hours later, and then another one a few thousand hours after that...
But of course, the main reason is the same for everybody on DIY Audio.com: fun!
Good day! This is fairly impromptu, but I'm amazed by the knowledge floating around here. If someone could comment, I'd really appreciate it.
I'm working on a project with a strong A/V component. My dad's office recently upgraded and let me have an EMP-600 minus bulb and ballast (missing).
I was wondering whether it would be smarter to buy a new bulb and ballast (around E220 from random websites) or whether a much cooler LED array was practical.
I read through the old posts, and it seems to have gone from proof-of-concept to debatably-worthy of use.
Prettiness isn't a factor, as all but the exit lens will be hidden.
Any info would be helpful,
Thanks,
Eric
I'm working on a project with a strong A/V component. My dad's office recently upgraded and let me have an EMP-600 minus bulb and ballast (missing).
I was wondering whether it would be smarter to buy a new bulb and ballast (around E220 from random websites) or whether a much cooler LED array was practical.
I read through the old posts, and it seems to have gone from proof-of-concept to debatably-worthy of use.
Prettiness isn't a factor, as all but the exit lens will be hidden.
Any info would be helpful,
Thanks,
Eric
Hi,
I think it might be better for you to find a new bulb and ballast because I don't think we'll see decent LED lighting for some time yet (hence the fact I haven't been on this thread for a while.)
I did buy a ballast from ywh a while back which works great. It's not amazingly compact, but smaller than some ballasts! He could also recommend the correct bulb to go with it. The main problem you'll have is if you don't have a reflector to put the new bulb into.
Then again, I found a genuine new lamp for my Dell projector on eBay for around £80, which isn't a bad price for a "proper" lamp. If you can get a ballast to match your projector's original bulb spec, it's worth trying to get hold of a genuine lamp really.
I've stalled on the LED project because in it's current state, it wouldn't be bright enough for anything much larger than a 20" image in complete darkness (in which case, you might as well watch a big TV!).
Many months ago, I did actually send off for the correct filters for combining the light from these K2 LEDs, but the company never replied (they probably have a Hotmail filter on!). So, I still haven't seen a full colour image from the current setup. Again though; although it might be impressive for an LED source, I don't think it would be practical for every day use. (The issue of combining multiple light sources into a narrow beam is THE major hurdle faced by all optical engineers with things like projectors - not that I'm an engineer by any means).
EDIT: Just read your bit about an LED array - I suppose if you wanted to put the work in, it's apparently quite possible to use a large LED array with a TFT panel and produce good results.....
http://www.hack247.co.uk/2006/08/14/diy-led-powered-lcd-projector/
(I think you'll need an account to view the photos on Lumenlab.)
OzOnE.
P.S. Ywh is the guy on the "I got my new lamp" thread who sells the replacement bulbs and ballasts.
I think it might be better for you to find a new bulb and ballast because I don't think we'll see decent LED lighting for some time yet (hence the fact I haven't been on this thread for a while.)
I did buy a ballast from ywh a while back which works great. It's not amazingly compact, but smaller than some ballasts! He could also recommend the correct bulb to go with it. The main problem you'll have is if you don't have a reflector to put the new bulb into.
Then again, I found a genuine new lamp for my Dell projector on eBay for around £80, which isn't a bad price for a "proper" lamp. If you can get a ballast to match your projector's original bulb spec, it's worth trying to get hold of a genuine lamp really.
I've stalled on the LED project because in it's current state, it wouldn't be bright enough for anything much larger than a 20" image in complete darkness (in which case, you might as well watch a big TV!).
Many months ago, I did actually send off for the correct filters for combining the light from these K2 LEDs, but the company never replied (they probably have a Hotmail filter on!). So, I still haven't seen a full colour image from the current setup. Again though; although it might be impressive for an LED source, I don't think it would be practical for every day use. (The issue of combining multiple light sources into a narrow beam is THE major hurdle faced by all optical engineers with things like projectors - not that I'm an engineer by any means).
EDIT: Just read your bit about an LED array - I suppose if you wanted to put the work in, it's apparently quite possible to use a large LED array with a TFT panel and produce good results.....
http://www.hack247.co.uk/2006/08/14/diy-led-powered-lcd-projector/
(I think you'll need an account to view the photos on Lumenlab.)
OzOnE.
P.S. Ywh is the guy on the "I got my new lamp" thread who sells the replacement bulbs and ballasts.
Here is an interesting diy LED mod for DLP projector.
http://www.elektor.com/magazines/2008/march/diy-led-projector.372582.lynkx
http://www.elektor.com/magazines/2008/march/diy-led-projector.372582.lynkx
Hi,
An interesting article, thanks for that, kl8ce!
Although quite informative, it's a bit disheartening for me to see that they're just using a fixed frequency for the colour wheel "emulator" pulse!
You see, in most DLP proectors, the colour wheel will actually change speed depending on the refresh rate of the input video signal. I spent many months of work on doing "proper" colour wheel emulation by actually decoding the colour wheel motor control chip data using an FPGA design. This allows for different input refresh rates (video sync rates.)
It's nice to see that it will work with a fixed frequency on some projectors though (plus, an AVR or PIC chip is quite a bit cheaper than an FPGA and easier to program IMHO.)
If you know the frequency of the input signal that you will likely always use (say 60Hz VGA), then it might work OK with some projectors to just use the same fixed frequency to send to the colour wheel opto.
Note: many projectors might use a 60Hz colour wheel rate for all input refresh rates between 60Hz and 120Hz (they just drop frames or repeat frames to match the differences.) In other words, the colour wheel speed won't neccessarily match the refresh rate on all projectors, especially on data / business projectors.
Most projectors use the Allegro A8902 motor control chip (or similar), and many projector chipsets out there will try to keep the colour wheel "in sync" with the pre-determined frequency from the control board. I found out that on my test projector, if the frequency of the colour wheel "simulator" wasn't exactly in phase with the expected pulses, it would cause flickering or corrupted images.
What the FPGA design does is to emulate a real colour wheel by taking the motor speed control data from the PJs control board and emulating the rotation / timing of the colour wheel. This allows the projector to keep the simulator pulses "in sync" (just as it would expect from the real colour wheel.) Plus, it also keeps up with refresh rate / wheel speed changes and can be programmed for very accurate timings for the LED colour changes etc.
Also, my current FPGA design allows you to fine tune the overall LED colour temperature to match the ideal colour calibration and colour efficiency. This can be controlled from a PC, or eventually using an on-screen menu generated by the FPGA itself. (it already has a VGA test pattern output!)
One thing about the Elektor design is that by using many LEDs and the "tin" light tunnel, it will be very inefficient in collecting the available light. Having said that, I don't think most people would care as long as the image was watchable and the LEDs didn't cost too much. The truth is, you won't get a particularly bright image unless you DO use multiple LEDs per colour (like Elektor have), but it will be terribly inefficient. Single LEDs are starting to produce more than 200 lumens per colour (fairly efficiently), so I'm sure LED projectors will be the next big thing in a few years.
The only other problem with this (apart from the efficiency) is that you may notice multiple images of each LED on the projected image. The extent of this will depend on the light tunnel, LED optics and projector design. The effect is usually more noticable when the projector is slightly out of focus....
When the projector is out-of-focus, the images usually look much worse than with the original lamp because there are now multilple point sources (LEDs). This reduces the "margin for error" slightly when focusing the image. In other words, most of your multiple LEDs will be outside of the usable collection area for the projector's optics and their light will be mostly wasted.
For example, I did try a very nice BL-3000 RGB "light engine" from Lamina Ceramics on a DLP projector, but the multiple images of the LED dies (dice?) appeared on the projected image and very few of the LEDs actually "fit" into the light path. These might work much better with LCD projectors, but I haven't bought LCD in years. I believe the BL-3000 series is now discontinued. They sell the Atlas RGB LEDs.....
http://www.laminaceramics.com/docs/AtlasDatasheet.pdf
But, a much cheaper option is a Prolight....
http://cgi.ebay.co.uk/1-PC-3W-PROLI...ageNameZWD2VQQcmdZViewItem?_trksid=p1638.m122
I used a Prolight for testing - there's no colour combining needed and they're easier to setup. Not amazingly bright though, you could just about watch Shrek on a 20" image in a completely dark room.
The Elektor article is definitely helpful in the fact that the projector they're using doesn't seem to care much about colour wheel sync. It probably uses a 100Hz colour wheel speed for most video refresh rates too.
It's a shame they don't give a more accurate idea of how bright it really is compared to the original lamp. (It might not be amazingly bright even with tons of Luxeon Rebel LEDs.)
Good to see a decent effort though. It has definitely spurred me on to get these dichroic filters ordered for my LED project. I've been meaning to order the correct filters for some time now, but I keep putting it off. (the filters aren't even that expensive.)
I still have the FPGA design, LED drivers, heatsinks and lenses in place, but I've yet to see the full potential of the three Luxeon K2 LEDs. (I can get partial results, but I ordered the wrong filters before, so I can't efficiently combine the available light into one beam.)
I like the idea of the Luxeon Rebel LEDs because they are almost as powerful as the K2s, but can be arranged much closer together.
If I get time (one day), I'll try to get some photos on here of my current LED setup.
OzOnE.
P.S. Jeez, I still type way too much!
This just in: http://catalog.osram-os.com/catalogue/catalogue.do?favOid=000000010001feb602880023&act=showBookmark
An interesting article, thanks for that, kl8ce!
Although quite informative, it's a bit disheartening for me to see that they're just using a fixed frequency for the colour wheel "emulator" pulse!
You see, in most DLP proectors, the colour wheel will actually change speed depending on the refresh rate of the input video signal. I spent many months of work on doing "proper" colour wheel emulation by actually decoding the colour wheel motor control chip data using an FPGA design. This allows for different input refresh rates (video sync rates.)
It's nice to see that it will work with a fixed frequency on some projectors though (plus, an AVR or PIC chip is quite a bit cheaper than an FPGA and easier to program IMHO.)
If you know the frequency of the input signal that you will likely always use (say 60Hz VGA), then it might work OK with some projectors to just use the same fixed frequency to send to the colour wheel opto.
Note: many projectors might use a 60Hz colour wheel rate for all input refresh rates between 60Hz and 120Hz (they just drop frames or repeat frames to match the differences.) In other words, the colour wheel speed won't neccessarily match the refresh rate on all projectors, especially on data / business projectors.
Most projectors use the Allegro A8902 motor control chip (or similar), and many projector chipsets out there will try to keep the colour wheel "in sync" with the pre-determined frequency from the control board. I found out that on my test projector, if the frequency of the colour wheel "simulator" wasn't exactly in phase with the expected pulses, it would cause flickering or corrupted images.
What the FPGA design does is to emulate a real colour wheel by taking the motor speed control data from the PJs control board and emulating the rotation / timing of the colour wheel. This allows the projector to keep the simulator pulses "in sync" (just as it would expect from the real colour wheel.) Plus, it also keeps up with refresh rate / wheel speed changes and can be programmed for very accurate timings for the LED colour changes etc.
Also, my current FPGA design allows you to fine tune the overall LED colour temperature to match the ideal colour calibration and colour efficiency. This can be controlled from a PC, or eventually using an on-screen menu generated by the FPGA itself. (it already has a VGA test pattern output!)
One thing about the Elektor design is that by using many LEDs and the "tin" light tunnel, it will be very inefficient in collecting the available light. Having said that, I don't think most people would care as long as the image was watchable and the LEDs didn't cost too much. The truth is, you won't get a particularly bright image unless you DO use multiple LEDs per colour (like Elektor have), but it will be terribly inefficient. Single LEDs are starting to produce more than 200 lumens per colour (fairly efficiently), so I'm sure LED projectors will be the next big thing in a few years.
The only other problem with this (apart from the efficiency) is that you may notice multiple images of each LED on the projected image. The extent of this will depend on the light tunnel, LED optics and projector design. The effect is usually more noticable when the projector is slightly out of focus....
When the projector is out-of-focus, the images usually look much worse than with the original lamp because there are now multilple point sources (LEDs). This reduces the "margin for error" slightly when focusing the image. In other words, most of your multiple LEDs will be outside of the usable collection area for the projector's optics and their light will be mostly wasted.
For example, I did try a very nice BL-3000 RGB "light engine" from Lamina Ceramics on a DLP projector, but the multiple images of the LED dies (dice?) appeared on the projected image and very few of the LEDs actually "fit" into the light path. These might work much better with LCD projectors, but I haven't bought LCD in years. I believe the BL-3000 series is now discontinued. They sell the Atlas RGB LEDs.....
http://www.laminaceramics.com/docs/AtlasDatasheet.pdf
But, a much cheaper option is a Prolight....
http://cgi.ebay.co.uk/1-PC-3W-PROLI...ageNameZWD2VQQcmdZViewItem?_trksid=p1638.m122
I used a Prolight for testing - there's no colour combining needed and they're easier to setup. Not amazingly bright though, you could just about watch Shrek on a 20" image in a completely dark room.
The Elektor article is definitely helpful in the fact that the projector they're using doesn't seem to care much about colour wheel sync. It probably uses a 100Hz colour wheel speed for most video refresh rates too.
It's a shame they don't give a more accurate idea of how bright it really is compared to the original lamp. (It might not be amazingly bright even with tons of Luxeon Rebel LEDs.)
Good to see a decent effort though. It has definitely spurred me on to get these dichroic filters ordered for my LED project. I've been meaning to order the correct filters for some time now, but I keep putting it off. (the filters aren't even that expensive.)
I still have the FPGA design, LED drivers, heatsinks and lenses in place, but I've yet to see the full potential of the three Luxeon K2 LEDs. (I can get partial results, but I ordered the wrong filters before, so I can't efficiently combine the available light into one beam.)
I like the idea of the Luxeon Rebel LEDs because they are almost as powerful as the K2s, but can be arranged much closer together.
If I get time (one day), I'll try to get some photos on here of my current LED setup.
OzOnE.
P.S. Jeez, I still type way too much!
This just in: http://catalog.osram-os.com/catalogue/catalogue.do?favOid=000000010001feb602880023&act=showBookmark
I have just found a infocus x2 for sale by me for $50 but it has a blown lamp. Being a college student I currently cannot afford to buy a buy the $270 lamp if I wanted to pick it up and fix it. I am looking into finding a way to make it work using some sort of other light source.
LED is the way to go for a projector if you are to ask me. It's not about heat, it's bulb life. If I can get a LED setup to give me 80-90% of the brightness of a bulb but at 50,000 hours instead of 4,000 then I would be ecstatic. The question is if this is possible yet though. I have been looking at these 250 lumen leds as a possible option. The x2 puts out 2000 lumens. This means that I would need 8-9 LEDs to get the same light output (these are guesstimates, I know little about light. Could I just hook up 8-9 of these as close as possible together and place them in the stock bulb reflector and put a small Fresnel somewhere in front of them to help reduce the problem of multiple points of light?
My other option is to try something like this.
http://www.instructables.com/id/Head-Light-Projector-Mod-V1.2/
Do you guys think it is worth trying to get LED's to work now that they are available with higher levels of output?
LED is the way to go for a projector if you are to ask me. It's not about heat, it's bulb life. If I can get a LED setup to give me 80-90% of the brightness of a bulb but at 50,000 hours instead of 4,000 then I would be ecstatic. The question is if this is possible yet though. I have been looking at these 250 lumen leds as a possible option. The x2 puts out 2000 lumens. This means that I would need 8-9 LEDs to get the same light output (these are guesstimates, I know little about light. Could I just hook up 8-9 of these as close as possible together and place them in the stock bulb reflector and put a small Fresnel somewhere in front of them to help reduce the problem of multiple points of light?
My other option is to try something like this.
http://www.instructables.com/id/Head-Light-Projector-Mod-V1.2/
Do you guys think it is worth trying to get LED's to work now that they are available with higher levels of output?
Led projector update
"It's not about heat, it's bulb life."
Actually with the latest arc lamp prices it's all about heat/noise rather than price/lamp life. You need to hunt bargains on ebay or try a deal from China/ywh though.
"This means that I would need 8-9 LEDs to get the same light output"
If only things were that simple!
Right now I get about 8 lumens from the 150lm I drive the led to. And that is with fine optics, because light collection is the challenge. The image is good in the dark, and if I keep it less than 1m I can even follow it with some light on. The upside is the damn thing is pretty much heat/noiseless.
Reallistically I could probably approach 20lm with some effort, but it would still be a far cry from emission displays, light and convenience wise. And they announced 150lm led projectors, so it's just a matter of time. Meanwhile Guy is right: the arc rules the projection world. Non laser leds can't touch its luminance.
Nice to see you still around ozone. Have you measured your light output?
"It's not about heat, it's bulb life."
Actually with the latest arc lamp prices it's all about heat/noise rather than price/lamp life. You need to hunt bargains on ebay or try a deal from China/ywh though.
"This means that I would need 8-9 LEDs to get the same light output"
If only things were that simple!
Right now I get about 8 lumens from the 150lm I drive the led to. And that is with fine optics, because light collection is the challenge. The image is good in the dark, and if I keep it less than 1m I can even follow it with some light on. The upside is the damn thing is pretty much heat/noiseless.
Reallistically I could probably approach 20lm with some effort, but it would still be a far cry from emission displays, light and convenience wise. And they announced 150lm led projectors, so it's just a matter of time. Meanwhile Guy is right: the arc rules the projection world. Non laser leds can't touch its luminance.
Nice to see you still around ozone. Have you measured your light output?
ballast bypass on Lp120
Hi there,
You guys seem to know a lot about projector ballasts and I wondered if you could help me. I'm trying to get an Infocus LP120 working without the ballast so I can make a LED projector to take camping.
I can get the thing to work using a 100ohm resister instead of bulb but thats not ideal as the damn thing glows red hot.
I've traced the lead from the Phillips ballast to the circuit and tried shorting the opto coupler to make it think the bulb is on but to no avail. Theres a 5 pin connection from the logic board to the ballast and , pin 1&2 I think are the 'bulb is ok' signal from the ballast. Pin 3 is GND gnd and 4 and 5 connect to pin 2 of the other 2 opto coupler (the diode side to presumable telling the ballast when to strike and something else).
heres some photos
http://www.flickr.com/photos/51328142@N00
THis has been bugging the hell out of me for ages now.
I reckon the next thing I'll do is put some LEDs on the DIODE side of the OCs and start the PJ up with the resistor or bulb and see what they tell me.
Many thanks
Gav
Hi there,
You guys seem to know a lot about projector ballasts and I wondered if you could help me. I'm trying to get an Infocus LP120 working without the ballast so I can make a LED projector to take camping.
I can get the thing to work using a 100ohm resister instead of bulb but thats not ideal as the damn thing glows red hot.
I've traced the lead from the Phillips ballast to the circuit and tried shorting the opto coupler to make it think the bulb is on but to no avail. Theres a 5 pin connection from the logic board to the ballast and , pin 1&2 I think are the 'bulb is ok' signal from the ballast. Pin 3 is GND gnd and 4 and 5 connect to pin 2 of the other 2 opto coupler (the diode side to presumable telling the ballast when to strike and something else).
heres some photos
http://www.flickr.com/photos/51328142@N00
THis has been bugging the hell out of me for ages now.
I reckon the next thing I'll do is put some LEDs on the DIODE side of the OCs and start the PJ up with the resistor or bulb and see what they tell me.
Many thanks
Gav
These projector are basically computers running a program. On mine SC the OC output did the trick, but other models may need a special sequence and/or timing of the OC signaling.
The elegant way would be to "upgrade" the firmware. Mine has a connector I'm sure it's for service purposes, including reflashing. I wonder if we could interface that with a PC serial port. I'd like to get rid of the annoying 1 min switch on delay.
Try to find a service manual, including circuit schematics. I couldn't find mine (Toshiba TLP260), unless I was willing to buy :-(
The elegant way would be to "upgrade" the firmware. Mine has a connector I'm sure it's for service purposes, including reflashing. I wonder if we could interface that with a PC serial port. I'd like to get rid of the annoying 1 min switch on delay.
Try to find a service manual, including circuit schematics. I couldn't find mine (Toshiba TLP260), unless I was willing to buy :-(
LED & Alternative Projector Light Sources
Hi everyone,
This is my first post, so apologies for any wrongdoings...
I have an ALLY PTV-01B, my first projector, which I'm modding with a new fan housing because it keeps getting too hot and switching off. I don't really think the fans fitted in it at manufacture are up to the job. When I've built and fitted the housing, I'll post on here about it if anyone's interested.
Thinking about possible solutions to this problem has prompted me to look into alternative light sources. I understand that it's necessary to have a single point of light, but I wonder if the LED's on a small array would be close enough to work.
I have read several posts on this site where people have said that LED's are not yet powerful enough to use, so I've been noseying around the internet and found these possible solutions:
Ostar Lighting LED - creating an LED spotlight bulb which is brighter than a 50 Watt halogen spot light with a lighting output in excess of 1,000 Lumens of cold white light:
http://www.reuk.co.uk/Osram-Ostar-Lighting-LED.htm
[1100 lumen LED's are now available on Ebay]
The Torch "World's Most Powerful Flashlight"
[Currently being reviewed by The Guinness Book of World Records, The Torch is the world's brightest and most powerful flashlight... 4100 lumens! The Torch uses a halogen light bulb rated at 100 Watts and runs on a custom built high voltage rechargeable battery.
http://www.wickedlasers.com/lasers/The_Torch-74-0.html
The Torch Light Bulb:
http://www.wickedlasers.com/lasers/The_Torch_Light_Bulb-76-29.html
Automotive Headlight Projector Mod V1.2:
http://www.instructables.com/id/Head-Light-Projector-Mod-V1.2/
I'd very very grateful to any of you knowledgeable people who would be kind enough to provide me with some advice on the posibilities of using any of the above.
Lastly, how do 'Lumens' equate to ANSI Lumens?
Best wishes
Tony
Hi everyone,
This is my first post, so apologies for any wrongdoings...
I have an ALLY PTV-01B, my first projector, which I'm modding with a new fan housing because it keeps getting too hot and switching off. I don't really think the fans fitted in it at manufacture are up to the job. When I've built and fitted the housing, I'll post on here about it if anyone's interested.
Thinking about possible solutions to this problem has prompted me to look into alternative light sources. I understand that it's necessary to have a single point of light, but I wonder if the LED's on a small array would be close enough to work.
I have read several posts on this site where people have said that LED's are not yet powerful enough to use, so I've been noseying around the internet and found these possible solutions:
Ostar Lighting LED - creating an LED spotlight bulb which is brighter than a 50 Watt halogen spot light with a lighting output in excess of 1,000 Lumens of cold white light:
http://www.reuk.co.uk/Osram-Ostar-Lighting-LED.htm
[1100 lumen LED's are now available on Ebay]
The Torch "World's Most Powerful Flashlight"
[Currently being reviewed by The Guinness Book of World Records, The Torch is the world's brightest and most powerful flashlight... 4100 lumens! The Torch uses a halogen light bulb rated at 100 Watts and runs on a custom built high voltage rechargeable battery.
http://www.wickedlasers.com/lasers/The_Torch-74-0.html
The Torch Light Bulb:
http://www.wickedlasers.com/lasers/The_Torch_Light_Bulb-76-29.html
Automotive Headlight Projector Mod V1.2:
http://www.instructables.com/id/Head-Light-Projector-Mod-V1.2/
I'd very very grateful to any of you knowledgeable people who would be kind enough to provide me with some advice on the posibilities of using any of the above.
Lastly, how do 'Lumens' equate to ANSI Lumens?
Best wishes
Tony
Lumens = ANSI Lumens
The real problem is the ratio of lumens in to lumens on the screen: With 20000 lumens from a MH arc lamp as the input, an LCD projector might only put 200 lumens on the screen. Everything in the optical path absorbs or reflects some of the light. Most home-built projectors lose a lot of light just getting to a set of aligned rays going through the LCD pixels. Then the LCD color filters lose at least 2/3 of the light because each pixel filter rejects the other two colors.
Running LED light through a standard LCD is going to give you the same amount of loss, so a usable LED projector will need at least 10000 lumens with a reasonable balance of red, green, and blue bands that can get through the LCD filters. One good thing about LEDs is they come in packages designed to send all of the light out the front in a narrow beam. That means you don't need a reflector behind them like you do with MH.
I have done experiments with multiple light sources, and it looks pretty bad. I don't think you can use a lot of LEDs to emulate a point source lamp. The optics don't work, so you get most of the light failing to get through the projection lens. Try some ray tracing yourself and you will see this.
You also get a pattern of bright and dark areas on the screen because some of the pixels get light from only one lamp, and some get light from two or more lamps. It would be very difficult to get the same amount of light to each pixel using multiple light sources. Of course, a standard MH homebuilt projector does have quite a bit of variation in the amount of light from the center pixels to the corners (like maybe 2:1!) but the change is gradual so you can't see any distracting repeating pattern.
I think the ultimate LED projector will actually use R, G, and B laser diodes with a fancy dichroic optical combiner that makes the three beams all appear to come from the same very small spot. (Can't be done with white beams.) It will also use a monochrome LCD or DLP, and pulse the laser diodes to work like a DLP colorwheel. Then there would be no LCD color filters to suck up the lumens. As soon as we can buy green and blue laser diodes off the shelf like we can red, we will be in business.
The real problem is the ratio of lumens in to lumens on the screen: With 20000 lumens from a MH arc lamp as the input, an LCD projector might only put 200 lumens on the screen. Everything in the optical path absorbs or reflects some of the light. Most home-built projectors lose a lot of light just getting to a set of aligned rays going through the LCD pixels. Then the LCD color filters lose at least 2/3 of the light because each pixel filter rejects the other two colors.
Running LED light through a standard LCD is going to give you the same amount of loss, so a usable LED projector will need at least 10000 lumens with a reasonable balance of red, green, and blue bands that can get through the LCD filters. One good thing about LEDs is they come in packages designed to send all of the light out the front in a narrow beam. That means you don't need a reflector behind them like you do with MH.
I have done experiments with multiple light sources, and it looks pretty bad. I don't think you can use a lot of LEDs to emulate a point source lamp. The optics don't work, so you get most of the light failing to get through the projection lens. Try some ray tracing yourself and you will see this.
You also get a pattern of bright and dark areas on the screen because some of the pixels get light from only one lamp, and some get light from two or more lamps. It would be very difficult to get the same amount of light to each pixel using multiple light sources. Of course, a standard MH homebuilt projector does have quite a bit of variation in the amount of light from the center pixels to the corners (like maybe 2:1!) but the change is gradual so you can't see any distracting repeating pattern.
I think the ultimate LED projector will actually use R, G, and B laser diodes with a fancy dichroic optical combiner that makes the three beams all appear to come from the same very small spot. (Can't be done with white beams.) It will also use a monochrome LCD or DLP, and pulse the laser diodes to work like a DLP colorwheel. Then there would be no LCD color filters to suck up the lumens. As soon as we can buy green and blue laser diodes off the shelf like we can red, we will be in business.
Thanks Guy and carpow,
Well, the Ally is supposed to be 1200 lumens - am I right in assuming that is measured from the lamp and not the screen?
The LED I saw on Ebay is 1100 - would that make much difference? The halogen bulb is 4100 lumens, which must certainly be more than bright enough for home cinema. I don't know about the car headlight idea.
Do you think it would be practical to use 'The Torch' bulb and a suitable power supply and cooling, or a powerful LED, such as to one on Ebay or the one that carpow has kindly uploaded a picture of? - Which, btw, I'd like a link to more information please!
What I'm looking for here is some practical advice on which, if any, of the methods I posted about will be suitable for me to adapt my projector to use, once the two lamps I have for it are used up.
I'm already making what I think will be a very adequate cooling system [4 x 120mm silent fans] and I think it would be enough to cool the 'Torch' bulb, mounted on an aluminium heatsink, which, with it's single point of light, would be ideal.
Regarding the LED option, how close do the individual elements have to be for it to be considered a single point of light?
Well, the Ally is supposed to be 1200 lumens - am I right in assuming that is measured from the lamp and not the screen?
The LED I saw on Ebay is 1100 - would that make much difference? The halogen bulb is 4100 lumens, which must certainly be more than bright enough for home cinema. I don't know about the car headlight idea.
Do you think it would be practical to use 'The Torch' bulb and a suitable power supply and cooling, or a powerful LED, such as to one on Ebay or the one that carpow has kindly uploaded a picture of? - Which, btw, I'd like a link to more information please!
What I'm looking for here is some practical advice on which, if any, of the methods I posted about will be suitable for me to adapt my projector to use, once the two lamps I have for it are used up.
I'm already making what I think will be a very adequate cooling system [4 x 120mm silent fans] and I think it would be enough to cool the 'Torch' bulb, mounted on an aluminium heatsink, which, with it's single point of light, would be ideal.
Regarding the LED option, how close do the individual elements have to be for it to be considered a single point of light?
Ok now on the led vs MH comparing output in Lumens is like comparing
apples and oranges
a lumen is a measurement of luminous flux (which mean that it is a measurement of how much Luminous intensity(candela) per(*) a unit of Steradian (which is some weird way to measure how much of a sphere you are going through and is basically a weird angular measurement)
because of this measureing of the fact that lumen are based on the angle of emitting light using lumens to measure LEDs is not an accurate way to compare them to MH
what aught to be measured is how many cds or (mcd) for LEDs per a m^2 goes through the lcd now there is now real name for that unit but i think that a mcd/m^2 which measures the amount of luminous intensity (brightness) per an area of our LCD
apples and oranges
a lumen is a measurement of luminous flux (which mean that it is a measurement of how much Luminous intensity(candela) per(*) a unit of Steradian (which is some weird way to measure how much of a sphere you are going through and is basically a weird angular measurement)
because of this measureing of the fact that lumen are based on the angle of emitting light using lumens to measure LEDs is not an accurate way to compare them to MH
what aught to be measured is how many cds or (mcd) for LEDs per a m^2 goes through the lcd now there is now real name for that unit but i think that a mcd/m^2 which measures the amount of luminous intensity (brightness) per an area of our LCD
MH lamps generally send light in all directions, with just the shadow of the electrodes or screw base blocking the output. LEDs send light in at most a half-sphere, but most of them are encapsulated in a plastic condensor lens package so the large cone of rays is refracted into a narrower cone. You can buy wide-cone LEDs and you can buy narrow cone LEDs, often with the same guts but different packages.
Lumens is the measurement of the total amount of light coming out of the device, no matter what the angle of the cone is, or even the distance of the measurement. Lux is the measure of lumens per square meter, and will decrease with the square of the distance.
Projectors that use MH lamps always include a reflector to direct the light into a cone of the desired shape. This mostly negates the problem of the light going off in all (unwanted) directions. A really good eliptical reflector made from polished aluminum can get 90% of the light where you want it. A silver-coated reflector can acheive over 95%!
So it is fair to compare the lumens output by MH lamps and LEDs, assuming you used an LED that had exactly the cone you needed for your design.
As for how close multiple light sources need to be so you don't see a light & dark pattern on the screen: I think that would be near the size of the pixels on the screen times the projection size ratio. (lamps-to-lens/lens-to-screen) If the distance between LEDs is large enough so that some screen pixels are lit by one LED and others are lit by two or more, then you will be able to see the pattern on the screen. The reason you don't see a pattern with a MH arc is not that the arc length is tiny, but rather because it's light output is continuous over the whole length and width of the arc. (There are no patterns.) That is not to say the brightness of the arc is completely uniform, because its not. But the change in brightness is smooth from any part of the arc to an adjacent part. (But you should know that a $65 store-lighting MH lamp may have an arc length of 25-35 mm, while a $250 projection MH lamp will have an arc length more like 5 mm.)
Of course, once you make an array of 640 by 480 LEDs (or more), you might as well just use them as the image generating elements instead of an LCD.
You might also be interested to know that I started with a 20000 lumen MH lamp, projecting a 95" diagonal image. When I changed to a 33000 lumen lamp, I was much happier with the image. If you use a 5000 lumen lamp, you won't be very happy with an image larger than about 40".
Lumens is the measurement of the total amount of light coming out of the device, no matter what the angle of the cone is, or even the distance of the measurement. Lux is the measure of lumens per square meter, and will decrease with the square of the distance.
Projectors that use MH lamps always include a reflector to direct the light into a cone of the desired shape. This mostly negates the problem of the light going off in all (unwanted) directions. A really good eliptical reflector made from polished aluminum can get 90% of the light where you want it. A silver-coated reflector can acheive over 95%!
So it is fair to compare the lumens output by MH lamps and LEDs, assuming you used an LED that had exactly the cone you needed for your design.
As for how close multiple light sources need to be so you don't see a light & dark pattern on the screen: I think that would be near the size of the pixels on the screen times the projection size ratio. (lamps-to-lens/lens-to-screen) If the distance between LEDs is large enough so that some screen pixels are lit by one LED and others are lit by two or more, then you will be able to see the pattern on the screen. The reason you don't see a pattern with a MH arc is not that the arc length is tiny, but rather because it's light output is continuous over the whole length and width of the arc. (There are no patterns.) That is not to say the brightness of the arc is completely uniform, because its not. But the change in brightness is smooth from any part of the arc to an adjacent part. (But you should know that a $65 store-lighting MH lamp may have an arc length of 25-35 mm, while a $250 projection MH lamp will have an arc length more like 5 mm.)
Of course, once you make an array of 640 by 480 LEDs (or more), you might as well just use them as the image generating elements instead of an LCD.
You might also be interested to know that I started with a 20000 lumen MH lamp, projecting a 95" diagonal image. When I changed to a 33000 lumen lamp, I was much happier with the image. If you use a 5000 lumen lamp, you won't be very happy with an image larger than about 40".
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