An idea about Projectors and Sunlight

[HDs suck]

I have been trying to think of a solution that would reduce the amount of power a projector bulb would have to produce to displace sunlight in an open area, when an idea hit me that i would have absolutely no idea how to answer or even begin to research. Would it be possible to concentrate the light coming from the sun into a lens that shot through the projector, making a bright image bright enough to see easily during daylight? Obviously this would require some sort of complicated solar panels that redirected light into a single beam appropriate for the projector, rendering the device a relatively stationary contraption. Does anyone have thoughts? It's scary to start a new topic in here, but I'd really like to see what you guys would have to say. Care to contribute?

 

[CycloWizard]

I'm not necessarily sure what you're after. Let me know if this is the wrong translation. You want to collect sunlight from an area and somehow focus it to increase the intensity? This can certainly be done using existing technologies and is one form of solar power generation that has been available for some time.

As for whether you could illuminate an object such that it stood out from its surroundings, this isn't a technical problem so much as a physiological one. On a bright sunny day, the photoreceptors in your eye are virtually saturated by bright objects. Raising the intensity further would have no apparent visual effect since your eye literally can't convert the photons to action potentials at a higher rate. Thus, though the actual intensity would be higher, the apparent intensity would be unchanged.

 

[Rike]

Originally posted by: HDs suck
I have been trying to think of a solution that would reduce the amount of power a projector bulb would have to produce to displace sunlight in an open area, when an idea hit me that i would have absolutely no idea how to answer or even begin to research. Would it be possible to concentrate the light coming from the sun into a lens that shot through the projector, making a bright image bright enough to see easily during daylight? Obviously this would require some sort of complicated solar panels that redirected light into a single beam appropriate for the projector, rendering the device a relatively stationary contraption. Does anyone have thoughts? It's scary to start a new topic in here, but I'd really like to see what you guys would have to say. Care to contribute?

I have no idea about how you might do this but I think what you are getting at is a method by which you would use redirected sunlight as the light source for image projection. Is that correct?

 

[CycloWizard]

Originally posted by: Rike
I have no idea about how you might do this but I think what you are getting at is a method by which you would use redirected sunlight as the light source for image projection. Is that correct?

Concave mirrors to collect the light and redirect it into a collimating lens. Easier said than done, but conceptually very simple.

 

[HDs suck]

Originally posted by: Rike

Originally posted by: HDs suck
I have been trying to think of a solution that would reduce the amount of power a projector bulb would have to produce to displace sunlight in an open area, when an idea hit me that i would have absolutely no idea how to answer or even begin to research. Would it be possible to concentrate the light coming from the sun into a lens that shot through the projector, making a bright image bright enough to see easily during daylight? Obviously this would require some sort of complicated solar panels that redirected light into a single beam appropriate for the projector, rendering the device a relatively stationary contraption. Does anyone have thoughts? It's scary to start a new topic in here, but I'd really like to see what you guys would have to say. Care to contribute?

I have no idea about how you might do this but I think what you are getting at is a method by which you would use redirected sunlight as the light source for image projection. Is that correct?

That is exactly what I mean, and my conceptual use would be to channel that light into a projector for an easily visible outdoor projection.

 

[Cogman]

CycloWizard I disagree about the photo receptors being overly saturated. Even at a bright sunny day, when you look at the sun, you can definitely tell a difference between it and say a white sheet in the sun.

I can see two problems right off the bat. The first is that the concave mirror will have to be fairly big in order for the projection to be visible. Projector lights are bright, and since you are in daylight you have to be brighter. My rough guess is that it should be somewhere around 1/4 to 1/2 the size of the image that you are trying to project. A monster.

The next problem, and probably the more serious one, is that with an image that bright, how do you keep from burning a hole through whatever material you use? Even a small magnifying glass (3 inch) will burn a hole in almost anything. You're going to need a much bigger one.

Seriously, you are going to have big issues with things spontaneously lighting on fire because of how hot the focused beam will be to make the image bright enough. (as channeling light implies filtering light which = absorbing energy). I don't know how this could work. Probably you would need something like a laser projector and Solar cells, simple lenses just wont cut it.

 

[CycloWizard]

Originally posted by: Cogman
CycloWizard I disagree about the photo receptors being overly saturated. Even at a bright sunny day, when you look at the sun, you can definitely tell a difference between it and say a white sheet in the sun.

The action potential firing rate follows a sigmoidal curve with respect to intensity (really, the log of intensity). On a bright sunny day, you're near the saturation portion of the curve such that the sensitivity of your eye is diminished. I'm not saying that his projector won't make any difference, but it's certainly not going to be anything like a spotlight at night or in a dark theater.

I can see two problems right off the bat. The first is that the concave mirror will have to be fairly big in order for the projection to be visible. Projector lights are bright, and since you are in daylight you have to be brighter. My rough guess is that it should be somewhere around 1/4 to 1/2 the size of the image that you are trying to project. A monster.

The next problem, and probably the more serious one, is that with an image that bright, how do you keep from burning a hole through whatever material you use? Even a small magnifying glass (3 inch) will burn a hole in almost anything. You're going to need a much bigger one.

Seriously, you are going to have big issues with things spontaneously lighting on fire because of how hot the focused beam will be to make the image bright enough. (as channeling light implies filtering light which = absorbing energy). I don't know how this could work. Probably you would need something like a laser projector and Solar cells, simple lenses just wont cut it.

It depends on how long he's going to use it for and what he wants to project onto. If he just wants it on a screen somewhere, the screen could be actively cooled. Even a lens can be cooled. If he just wants to use it for a few seconds at a time, then it wouldn't really be an issue. But using solar cells would necessarily result in a loss of intensity because you are adding layers of inefficiency to the process (converting the photons to electricity, then back to photons through heat, even if there is no chemical intermediate). Since most solar cells are still far less than 10% efficient at converting the energy of a photon into electricity, the mirror is a much simpler, cost-effective alternative that takes up less space. The size of the mirror is easy to compute if you know the intensity of the sun (generally on the order of 10^9 photons/cm^2/s IIRC) and the desired image size and intensity. It's simply a ratio A_1*I_1=A_2*I_2, where A is the area and I is the intensity.

 

[Cogman]

Originally posted by: CycloWizard

Originally posted by: Cogman
CycloWizard I disagree about the photo receptors being overly saturated. Even at a bright sunny day, when you look at the sun, you can definitely tell a difference between it and say a white sheet in the sun.

The action potential firing rate follows a sigmoidal curve with respect to intensity (really, the log of intensity). On a bright sunny day, you're near the saturation portion of the curve such that the sensitivity of your eye is diminished. I'm not saying that his projector won't make any difference, but it's certainly not going to be anything like a spotlight at night or in a dark theater.

I can see two problems right off the bat. The first is that the concave mirror will have to be fairly big in order for the projection to be visible. Projector lights are bright, and since you are in daylight you have to be brighter. My rough guess is that it should be somewhere around 1/4 to 1/2 the size of the image that you are trying to project. A monster.

The next problem, and probably the more serious one, is that with an image that bright, how do you keep from burning a hole through whatever material you use? Even a small magnifying glass (3 inch) will burn a hole in almost anything. You're going to need a much bigger one.

Seriously, you are going to have big issues with things spontaneously lighting on fire because of how hot the focused beam will be to make the image bright enough. (as channeling light implies filtering light which = absorbing energy). I don't know how this could work. Probably you would need something like a laser projector and Solar cells, simple lenses just wont cut it.

It depends on how long he's going to use it for and what he wants to project onto. If he just wants it on a screen somewhere, the screen could be actively cooled. Even a lens can be cooled. If he just wants to use it for a few seconds at a time, then it wouldn't really be an issue. But using solar cells would necessarily result in a loss of intensity because you are adding layers of inefficiency to the process (converting the photons to electricity, then back to photons through heat, even if there is no chemical intermediate). Since most solar cells are still far less than 10% efficient at converting the energy of a photon into electricity, the mirror is a much simpler, cost-effective alternative that takes up less space. The size of the mirror is easy to compute if you know the intensity of the sun (generally on the order of 10^9 photons/cm^2/s IIRC) and the desired image size and intensity. It's simply a ratio A_1*I_1=A_2*I_2, where A is the area and I is the intensity.

Well, if you just want a pure light projected onto a screen, I would agree with you, but most likely he wants an image that is associated with the light. The only way that could occur with mirrors is for the light from the projector to pass through some sort of filter layer. That filter is going to be subjected to the light at its most intense point. Even with cooling you aren't going to have more then a couple of milliseconds before the thing bursts into flames or melts.

 

[Modelworks]

Another issue to consider is that sunlight contains many other spectrums besides visible light. Sending concentrated UV light through a projector might not be good for the projector. I don't know that anyone has done testing on the lifespan of LCD and UV/IR light. Some plastics and paints fail rapidly in UV light. The other problem is color. Sunlight is not a pure white light , it has many different colors depending on the time of day, atmosphere, so you would need some way of auto adjusting the output color based on a sample of the current sunlight color.

Overall I think you would be better just finding a shady spot with a good projector

 

[CycloWizard]

Originally posted by: Cogman
Well, if you just want a pure light projected onto a screen, I would agree with you, but most likely he wants an image that is associated with the light. The only way that could occur with mirrors is for the light from the projector to pass through some sort of filter layer. That filter is going to be subjected to the light at its most intense point. Even with cooling you aren't going to have more then a couple of milliseconds before the thing bursts into flames or melts.

He use lens arrays rather than filters to create the image. The problem is way too poorly defined (and, in my opinion, not very well conceived) to worry about the fine details of how to do it.

 

[Cogman]

Originally posted by: CycloWizard

Originally posted by: Cogman
Well, if you just want a pure light projected onto a screen, I would agree with you, but most likely he wants an image that is associated with the light. The only way that could occur with mirrors is for the light from the projector to pass through some sort of filter layer. That filter is going to be subjected to the light at its most intense point. Even with cooling you aren't going to have more then a couple of milliseconds before the thing bursts into flames or melts.

He use lens arrays rather than filters to create the image. The problem is way too poorly defined (and, in my opinion, not very well conceived) to worry about the fine details of how to do it.

So are you saying use some sort of spinning prisms somewhat like DLP does (only it uses mirrors) to get the desired output?

That could be interesting.

 

[Biftheunderstudy]

There was a research group a while back that was using optical fibres to transport sunlight around. The idea was to bring natural sunlight into office buildings. It would be relatively easy to put a fibre coupler (albeit expensive) into the projector. To get rid of the UV, just put a coating on the parabolic mirror. Ideally you could coat 3 mirrors for each colour and combine them in the projector.

 

[Modelworks]

Originally posted by: Biftheunderstudy
There was a research group a while back that was using optical fibres to transport sunlight around. The idea was to bring natural sunlight into office buildings. It would be relatively easy to put a fibre coupler (albeit expensive) into the projector. To get rid of the UV, just put a coating on the parabolic mirror. Ideally you could coat 3 mirrors for each colour and combine them in the projector.

There are quite a few products on the market to do this.
They use a dome on the roof to capture the light then it goes down a tube the is highly polished on the inside which attaches to lens in the building to disperse the light.
http://www.sun-dome.com/