I know a this topic has been discussed time and time again and people who have played about with these have confirmed that they are simply not bright enough.
Others go on about how the light source is spreaded and not a point like the MH arcs.
Now I can't help thinking that those who have plyed about with LEDs as light source would have not been able to collect enough of the light with the fresnals as the most probably got the light from the center of the array and lost the power of LED around the edges.
Now if we was to use another fresnal or some wide enough convex lens to collect the light to a point and position this (virtual) point where the arc of the lamp is mant to be rather than focusing on the postioning of the LED array, would in effect will we not be getting a point light source which can be reduced to less than a milimetre?
Others go on about how the light source is spreaded and not a point like the MH arcs.
Now I can't help thinking that those who have plyed about with LEDs as light source would have not been able to collect enough of the light with the fresnals as the most probably got the light from the center of the array and lost the power of LED around the edges.
Now if we was to use another fresnal or some wide enough convex lens to collect the light to a point and position this (virtual) point where the arc of the lamp is mant to be rather than focusing on the postioning of the LED array, would in effect will we not be getting a point light source which can be reduced to less than a milimetre?
LEDs can and do work. I play with them all the time and I have 2 in the mail heading this way. Array's wont work as well and 1 bright LED. Right now as I type this I am watching a movie in a commercial projector that is powered by a custom LED setup. The LED is only rated for 100 lumens. The image is dim but watchable at 82 inches wide in the dark. The LEDs I have coming is the same size but rated for 1000 and 3000 Lumens. If 1 100 lumen LED gives me a watchable image the 3000 will for sure be on par with alot of other DIY setups. Its not gonna be factory bright but maybe 300-400 lumens at the screen. At 48 inches the projection is fantastic. I will post more when I get my higher powered LED's
Note
This does not work well with DLP projectors I have yet to find a way to use an led with that blasted color wheel. I can get small dim images but 66% of the light is blocked when filtering the RGB colors. DLP might have better contrast ratios but LCD is much more light efficient. 3chip DLP projectors may prove better but they are way over priced still.
Note
This does not work well with DLP projectors I have yet to find a way to use an led with that blasted color wheel. I can get small dim images but 66% of the light is blocked when filtering the RGB colors. DLP might have better contrast ratios but LCD is much more light efficient. 3chip DLP projectors may prove better but they are way over priced still.
I have been reading extensively on this subject for the past few days and it looks to me like there are two approaches to LED lighting.
Point source:
Using a single, very high power LED to act as a point source is the same idea as the arc lamp in a conventional projector. You get very even brightness since your theoretical point source is infinitely small and therefore compeltely evenly lit accross the whole source. The problem is that single LED's are not as bright as conventional lamps and very carefully designed optics have to be used to get the maximum amount of light to the screen.
Array source:
Using many LED's in an array to replicate the parallel light rays you hope to get through your LCD. Here brightness is not so much of a problem because you can use as many LED's as your wallet allows (as long as you have the patince to solder them all). The problem here is creating an even spread of light because we dont have the perfectly even infinitely small point anymore, we have a number of individual sources which overlap. This type of light source requires carefully designed optics to try and even the spread of light without losing too much in the process.
Option 1 has been tried with good results but I have seen nothing which is really bright enough to compare to a standard projector. Cheap though.
Option 2 has also been tried with good results, usually much higher brightness than the point source approaches.
http://www.lumenlab.com/forums/index.php?showtopic=24619
This guy has been the most successful that i have seen. He is using a conventional projector retrofitted with LED lighting. he has tried several different arrangements.
http://www.lumenlab.com/forums/index.php?showtopic=27877
This is one of the other more successful arrangements i have seen. Using a 50W LED array intended for street lighting.
The avenue i am currently investigating is similar to the second link possibly using a wide angle camera lens slightly out of focus to merge the individual elements of the LED array.
That shows the sort of results you can get with camera lenses. Thats a 180mm lens, from the photo i would guess hes about 5m or so from the wall. I want to play around with a wide angle, maybe 28mm focal length and see what sort of results can be achieved.
Point source:
Using a single, very high power LED to act as a point source is the same idea as the arc lamp in a conventional projector. You get very even brightness since your theoretical point source is infinitely small and therefore compeltely evenly lit accross the whole source. The problem is that single LED's are not as bright as conventional lamps and very carefully designed optics have to be used to get the maximum amount of light to the screen.
Array source:
Using many LED's in an array to replicate the parallel light rays you hope to get through your LCD. Here brightness is not so much of a problem because you can use as many LED's as your wallet allows (as long as you have the patince to solder them all). The problem here is creating an even spread of light because we dont have the perfectly even infinitely small point anymore, we have a number of individual sources which overlap. This type of light source requires carefully designed optics to try and even the spread of light without losing too much in the process.
Option 1 has been tried with good results but I have seen nothing which is really bright enough to compare to a standard projector. Cheap though.
Option 2 has also been tried with good results, usually much higher brightness than the point source approaches.
http://www.lumenlab.com/forums/index.php?showtopic=24619
This guy has been the most successful that i have seen. He is using a conventional projector retrofitted with LED lighting. he has tried several different arrangements.
http://www.lumenlab.com/forums/index.php?showtopic=27877
This is one of the other more successful arrangements i have seen. Using a 50W LED array intended for street lighting.
The avenue i am currently investigating is similar to the second link possibly using a wide angle camera lens slightly out of focus to merge the individual elements of the LED array.
That shows the sort of results you can get with camera lenses. Thats a 180mm lens, from the photo i would guess hes about 5m or so from the wall. I want to play around with a wide angle, maybe 28mm focal length and see what sort of results can be achieved.
What i meant by the LED array setup is as below. Basically capturing all the parallel rays of each leds an collecting it to a point source. Crazifunguy, could you provide me with the source for the 3000 Lumen LED that you are intending to use and how much are we looking at for that setup?
Attachments
I think you will find that due to the distances you are working with, you will not be able to focus an array of led's to a point like you want to.
The example as it was explained somewhere else, is using the Sun to burn a piece of paper.
The spot you use to burn the paper is not really a point, its a small image of the sun. The size of this image is found from the equation:
M = -i/o = h'/h
If the image and object are in the same medium it is just the image distance divided by the object distance.
So, back to the sun example, the distance from the sun to your lens is approximately
150 x 10 ^ 11 m
and the distance from your lens to your image is about 0.2m This means your magnification is roughly
-0.2/150 x 10 ^ 11 = -1.3 x 10 ^ -12
(with the negative sign indicating our image is inverted, which we dont really care about).
The diameter of the sun is roughly 1.4 x 10 ^ 9 m, so your image size is
1.4 x 10 ^ 9 x 1.3 x 10 ^ -12 = 0.001886 m = 1.86mm
Which seems about right.
Now we go to your example.
You have a light source which is maybe 100mm diameter at about 200mm from the lens. You want to focus it to a point about 50 mm on the other side of the lens. Your magnification is only 50/200 = 0.25 so the smallest you can make your 'point' is 100 * 0.25 = 25mm diameter.
The second problem is that its not actually a point source at all, its just a smaller image of your LED array. Its not really going to change anything because when you blow it up again on the screen, its still going to have all the uneven lighting that your original light source had.
The example as it was explained somewhere else, is using the Sun to burn a piece of paper.
The spot you use to burn the paper is not really a point, its a small image of the sun. The size of this image is found from the equation:
M = -i/o = h'/h
If the image and object are in the same medium it is just the image distance divided by the object distance.
So, back to the sun example, the distance from the sun to your lens is approximately
150 x 10 ^ 11 m
and the distance from your lens to your image is about 0.2m This means your magnification is roughly
-0.2/150 x 10 ^ 11 = -1.3 x 10 ^ -12
(with the negative sign indicating our image is inverted, which we dont really care about).
The diameter of the sun is roughly 1.4 x 10 ^ 9 m, so your image size is
1.4 x 10 ^ 9 x 1.3 x 10 ^ -12 = 0.001886 m = 1.86mm
Which seems about right.
Now we go to your example.
You have a light source which is maybe 100mm diameter at about 200mm from the lens. You want to focus it to a point about 50 mm on the other side of the lens. Your magnification is only 50/200 = 0.25 so the smallest you can make your 'point' is 100 * 0.25 = 25mm diameter.
The second problem is that its not actually a point source at all, its just a smaller image of your LED array. Its not really going to change anything because when you blow it up again on the screen, its still going to have all the uneven lighting that your original light source had.
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