After reading here and playing for awhile I figured I'd share my comments - and some findings
I've got my OHP running a 600W halogen - with that an old LCD panel from my old work laptop at 640X480 - the picture look much better than I expected - the response time is horrible but it works for Nesticle and playing excitebike and legend of zelda and such
So as I had a 250W Mogul Metal Halide with ballast setup available I figured I'd give it a try - modified for the big bulb, adjusted the lower fresnel spacing for the change in light source center and started testing. While the bulb seemed to get very bright once it warmed up after about 2 to 3 minutes the image was definately not as bright on the wall as the 600w halogen bulb (I have pics and can post a link or a website if needed). I'm sure part of it has to do with reflector quality because of the size of the MH mogul setup and the focus abilities of it from the virtual light source size (and that it doesnt act so well as a point source) - no reason to think that the relative polarization levels of the two sources are different is there?
Also the metal halide showed waves of light crossing the image (not sure if this is the flicker people reference, but this is a wave that starts at the top and moves to the bottom of the LCD maybe about 4 Hzs or so). I cant see this with the old presentation slides, but then the light is so bright that it would be washed out anyways, and its not apparent on very light areas of the LCD screen, but on the black backgrounds it definately stands out (is this common with MHs, just moguls, or maybe the low frequency of the LCD)?
Also while the Halogen caused the LCD to overheat and lose image in a few minutes the halogen ran cool enough to run constantly.
So ideally I prefer the halogen setup, if only because it is what works well for me now, if I could find a suitable IR reflector (nobody seems to stock low e glass locally - and I'm concerned on the nonlinearity of the visible glass transmission levels). I work with vacuum coatings (if anybody cares my focus is PVD for semiconductor but we have a whole division that does optical reflection / transmission coatings - actually we sell the equipment to do it), and I may just develop my own rejection/mirror filter (maybe 2 - 1 for <360nm, 1 for >780).
The next step is the real LCD but I've got to get past the light source and IR steps first.
I've got my OHP running a 600W halogen - with that an old LCD panel from my old work laptop at 640X480 - the picture look much better than I expected - the response time is horrible but it works for Nesticle and playing excitebike and legend of zelda and such
So as I had a 250W Mogul Metal Halide with ballast setup available I figured I'd give it a try - modified for the big bulb, adjusted the lower fresnel spacing for the change in light source center and started testing. While the bulb seemed to get very bright once it warmed up after about 2 to 3 minutes the image was definately not as bright on the wall as the 600w halogen bulb (I have pics and can post a link or a website if needed). I'm sure part of it has to do with reflector quality because of the size of the MH mogul setup and the focus abilities of it from the virtual light source size (and that it doesnt act so well as a point source) - no reason to think that the relative polarization levels of the two sources are different is there?
Also the metal halide showed waves of light crossing the image (not sure if this is the flicker people reference, but this is a wave that starts at the top and moves to the bottom of the LCD maybe about 4 Hzs or so). I cant see this with the old presentation slides, but then the light is so bright that it would be washed out anyways, and its not apparent on very light areas of the LCD screen, but on the black backgrounds it definately stands out (is this common with MHs, just moguls, or maybe the low frequency of the LCD)?
Also while the Halogen caused the LCD to overheat and lose image in a few minutes the halogen ran cool enough to run constantly.
So ideally I prefer the halogen setup, if only because it is what works well for me now, if I could find a suitable IR reflector (nobody seems to stock low e glass locally - and I'm concerned on the nonlinearity of the visible glass transmission levels). I work with vacuum coatings (if anybody cares my focus is PVD for semiconductor but we have a whole division that does optical reflection / transmission coatings - actually we sell the equipment to do it), and I may just develop my own rejection/mirror filter (maybe 2 - 1 for <360nm, 1 for >780).
The next step is the real LCD but I've got to get past the light source and IR steps first.
welcome dcarpa
I have the same type 600W Halogen blub in my OHP and yes the heat is intense. I have tried to put two 120v fans on the bulb for cooling. See pictures on page 2 of "Too bright Too Hot.
The only thing that might help is to build an enclouser and put the bulb / light engine on the back wall and put fans on the bottom and top. Heat rises right? Have the bottom one blowing in cool air and the top one drawing out the hot air.
As of now I do not have a 15" monitor to work with. I'm using an old passive matrix 7" LCD for test.
For a IR reflector (blocker) in the OHP, I don't have access to low-e glass here either but I am currently tring to "sandwich" a sheet of plexi glass between two sheets of clear glass.
Hope this helps.
🙂
I have the same type 600W Halogen blub in my OHP and yes the heat is intense. I have tried to put two 120v fans on the bulb for cooling. See pictures on page 2 of "Too bright Too Hot.
The only thing that might help is to build an enclouser and put the bulb / light engine on the back wall and put fans on the bottom and top. Heat rises right? Have the bottom one blowing in cool air and the top one drawing out the hot air.
As of now I do not have a 15" monitor to work with. I'm using an old passive matrix 7" LCD for test.
For a IR reflector (blocker) in the OHP, I don't have access to low-e glass here either but I am currently tring to "sandwich" a sheet of plexi glass between two sheets of clear glass.
Hope this helps.
🙂
Gotta be radiation
The heat cant be coming from convection since my LCD is isolated from the light source by the lenses, glass panel, etc. - and the glass panel it sits on stays cool - but i can feel my hand warm when placed just above it so it must primarily be the infrared radiation (also what I expected for this type of bulb and from what everybody else has experienced). Fans would help by introducing convection as a cooling method to the LCD but without getting rid of the infrared I doubt how successful that is going to be (but it is a much simpler method, just not as elegent). I think something like Thermashield made by ROSCO may work but it doesnt seem very workable for its size. I've also got plexiglass but its not gonna do the trick for me.
The heat cant be coming from convection since my LCD is isolated from the light source by the lenses, glass panel, etc. - and the glass panel it sits on stays cool - but i can feel my hand warm when placed just above it so it must primarily be the infrared radiation (also what I expected for this type of bulb and from what everybody else has experienced). Fans would help by introducing convection as a cooling method to the LCD but without getting rid of the infrared I doubt how successful that is going to be (but it is a much simpler method, just not as elegent). I think something like Thermashield made by ROSCO may work but it doesnt seem very workable for its size. I've also got plexiglass but its not gonna do the trick for me.
commercial infrared filters
I have seen (and thanks for the response dread) that Schott makes the KG series with the KG3 having the best IR response, and that is identical to the HOYA HA-30 and the Optima GRB3 filters - my main problem is that I cant find anything over 2" - one example is a company in CT that has the KG3 filters for $23 each
I may forced to just deposit my own filters on glass but I havent found the right stack and materials yet (from literature only) to deposit - if anyone knows what these films are and their thicknesses I'd love to now - if I find out i'll post
Indium Tin Oxide is commonly used - and then combined that with a low index material (like glass) can make a reflector but the stack is usually several layers and I dont want to reinvent the wheel.
I have seen (and thanks for the response dread) that Schott makes the KG series with the KG3 having the best IR response, and that is identical to the HOYA HA-30 and the Optima GRB3 filters - my main problem is that I cant find anything over 2" - one example is a company in CT that has the KG3 filters for $23 each
I may forced to just deposit my own filters on glass but I havent found the right stack and materials yet (from literature only) to deposit - if anyone knows what these films are and their thicknesses I'd love to now - if I find out i'll post
Indium Tin Oxide is commonly used - and then combined that with a low index material (like glass) can make a reflector but the stack is usually several layers and I dont want to reinvent the wheel.
water - that would be a big projector
Water asborbs infrared - the only problem is that it takes about 2meters of water to drop to 50% absorption at 650nm - that could be a bit much - unless it was a combined diy hot tub / projector
Water asborbs infrared - the only problem is that it takes about 2meters of water to drop to 50% absorption at 650nm - that could be a bit much - unless it was a combined diy hot tub / projector
Water absorbs almost all infrared with a wavelength of 2940 nm, it is certainly suitable for filtering infrared from a halogen lamp.
I have tested it with a 300 watt halogen light and a layer of water of about 3 cm.
Without the water you can easily set a black peace of paper on fire, with the water it doesn't even get warm.
I have tested it with a 300 watt halogen light and a layer of water of about 3 cm.
Without the water you can easily set a black peace of paper on fire, with the water it doesn't even get warm.
Hey i am a chemist so i thought about this. The problem is that water boils at 100 dergees and i think this can be reached easely. So i have been looking at other liquits and i believe glycerol (antifreeze) will also do the job.
arent we trying to filter NIR
I thought that if we assume the blackbody radiation for the lamp that the primary infrared would be around the 1000nm range - or the Near Infrared (NIR) which is up to about 1940 or - and that the halogen would peak in this NIR range (about 1000) and then decrease logarithmically or so and if this was the case then the higher wavelengths wouldnt be the main problem. I'll try and attach the water absorption profle showing that while it does effect the infrared the absorption gets stronger as it approaches over 2000 or 3000nm - while the radiation emission of a hot source would be just the opposite - Am I making too many assumptions on the radiation emission of the halogen
I thought that if we assume the blackbody radiation for the lamp that the primary infrared would be around the 1000nm range - or the Near Infrared (NIR) which is up to about 1940 or - and that the halogen would peak in this NIR range (about 1000) and then decrease logarithmically or so and if this was the case then the higher wavelengths wouldnt be the main problem. I'll try and attach the water absorption profle showing that while it does effect the infrared the absorption gets stronger as it approaches over 2000 or 3000nm - while the radiation emission of a hot source would be just the opposite - Am I making too many assumptions on the radiation emission of the halogen
Attachments
I couldn't found a realy great pic.
I think that in these cases we have to try it, its to difficult to predict the amount of ir what is filtered out.
An externally hosted image should be here but it was not working when we last tested it.
I think that in these cases we have to try it, its to difficult to predict the amount of ir what is filtered out.
The water heating up is not a problem at all, you can easily fix that with a pump, radiator and fan.
I have a watercooled pc, I used a radiator bought from a scrapyard for 10 euro.
Make sure you use the same kind of metal in your setup, is you use aluminum and copper, the aluminum will corrode.
Using some sort of anti-corrosion is not an option, unless you can find one that is transparant like water.
If you have a halogen lamp lying around, you can test it yourself with a glass of water.
I have a watercooled pc, I used a radiator bought from a scrapyard for 10 euro.
Make sure you use the same kind of metal in your setup, is you use aluminum and copper, the aluminum will corrode.
Using some sort of anti-corrosion is not an option, unless you can find one that is transparant like water.
If you have a halogen lamp lying around, you can test it yourself with a glass of water.
ethylene glycol is transparent they add dyes to it to give it colour. If you can get hold of ethylene glycol instead of radiator additives it will be clear.
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