Hi there all.
A quick question for the collective knowledge pool here at diyaudio......
When using an OHP, does the light have to come from a single source? I'm thinking of making a OHP/LCD system with a 3x4 array of 3W luxeon stars (total of 960 lumens)..... I'm not asking about whether or not the LEDs will be powerful enough, that's a seperate issue, what I'm asking is will I need any further optics to get it to work, or could I just put the array in the bottom of the OHP.
Thanks in advance,
forgieboy
A quick question for the collective knowledge pool here at diyaudio......
When using an OHP, does the light have to come from a single source? I'm thinking of making a OHP/LCD system with a 3x4 array of 3W luxeon stars (total of 960 lumens)..... I'm not asking about whether or not the LEDs will be powerful enough, that's a seperate issue, what I'm asking is will I need any further optics to get it to work, or could I just put the array in the bottom of the OHP.
Thanks in advance,
forgieboy
Sorry, upon rereading my post the question displays
a) a lack of understanding
b) a lack of effort in gaining understanding
My new and improved question is thus:
How big can the light source be? How big is the light source in a MH or halogen bulb? I'm talking about the area of the filament here....
a) a lack of understanding
b) a lack of effort in gaining understanding
My new and improved question is thus:
How big can the light source be? How big is the light source in a MH or halogen bulb? I'm talking about the area of the filament here....
OHP optics
OHPs use optics designed for a single light source at the focal point of the lower fresnel. It would not work with more than one light source.
But if you had thousands of narrow-angle LEDs pointing straight up, on a board the size of your panel, then you could remove the lower fresnel (keep the upper one), and just use those as the source of light through the LCD pixels. That could work, in regard to the light path.
The real problems with LEDs are:
1) They cost MUCH MUCH more than any other light source
2) They put out more waste heat than a MH bulb of the same light intensity
3) They are physically too big for the amount of light they put out, so you can't get enough of them on that board I mentioned
4) Most of the high-intensity white LEDs are really blue LEDs with a yellow phosphor. Looks white to us, but the yellow light will not get through an LCD's red and green filters.
5) They need a current limiting resistor for each individual LED. Their threshold voltages do not match perfectly. Without individual resistors, the LED with the lowest threshold will get all the current until it explodes, then the next, etc.
Other than that, if you can find a good source of free super high-intensity red, green, and blue LEDs, and you also get electricity for free, then it might be worth exploring.
Or you could make LED-backlit LCD glasses. That would work fine.
OHPs use optics designed for a single light source at the focal point of the lower fresnel. It would not work with more than one light source.
But if you had thousands of narrow-angle LEDs pointing straight up, on a board the size of your panel, then you could remove the lower fresnel (keep the upper one), and just use those as the source of light through the LCD pixels. That could work, in regard to the light path.
The real problems with LEDs are:
1) They cost MUCH MUCH more than any other light source
2) They put out more waste heat than a MH bulb of the same light intensity
3) They are physically too big for the amount of light they put out, so you can't get enough of them on that board I mentioned
4) Most of the high-intensity white LEDs are really blue LEDs with a yellow phosphor. Looks white to us, but the yellow light will not get through an LCD's red and green filters.
5) They need a current limiting resistor for each individual LED. Their threshold voltages do not match perfectly. Without individual resistors, the LED with the lowest threshold will get all the current until it explodes, then the next, etc.
Other than that, if you can find a good source of free super high-intensity red, green, and blue LEDs, and you also get electricity for free, then it might be worth exploring.
Or you could make LED-backlit LCD glasses. That would work fine.
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