Light emitting diodes, CCDs, CMOSs, and photovoltic cells among other things

Factual Questions
1

What are the functional differences and similarities between these four photoreactive components? Is it feasible or conceivable that in the near future (20-50 years) it will be possible to integrate into one unit, using these technologies or ones like them, a product that can simultaneously absorb sunlight on it’s backside as electricity while selectively reemitting absorbed spectrums from it’s front side?

That is, is the creation of a solar panel that can directly produce electricity from photonic reactions while simultaneously allowing for a selective filtering process so that an image may be emitted from the opposite side likely or even feasible with current or forseeable technology?

The main question here, I suppose, is this: If an LED will emit a specific spectrum when subjected to an electrical impulse without creating heat, can it be expected that when assaulted with the same spectrum it would emit an electrical impulse?

If you’ll follow me for a moment I believe you can understand what I’m getting at here. If we could create such a panel it would be realistic to assume that this panel could at any given time either be absorbing electricity from “thin air” (that is, produce electricity from photonic reaction), or displaying an image by selective filtering, much like reactive window tinting or sunglass tinting. Further, such a panel could be near transparent, by not filtering whatsoever (to be used as a window, perhaps), or black, by absorbing the full spectrum.

Even then, if radio waves, micro waves, x-rays, etcetera are all part of a single spectrum, would it be feasible to create an LED type diode for the full spectral range? What of lasers, that is, can we go beyond the visible range with lasers and create pinpoint magnetic sources projected at a distance, or so on or so forth?

If this makes no sense to you, I’m sorry, I tried. If it does, thank you for taking the time to let it make sense. I wish to preemptively thank everyone who takes the time to respond to these bizarre and possibly nonsensical questions, especially thanking those who impart in their answers useful or useable knowledge. While I may not reply to this thread again for some time, if at all, please rest assured that it will be read and understood and any information imparted dearly received.

Thank you again.

–Tim

2

I think I see what you’re saying here: You want a device, presumably in some sort of flat panel, which absorbs light on one side, and then selectively re-emits some or all of it on the other side. Right? There’s no reason it couldn’t be done, but it wouldn’t be as cool as it sounds. For starters, I don’t think that there’s any photovoltaic-type device currently which retains information about what direction light came from, so you couldn’t use this thing like a window. When you look at a window, what you see through it depends on what direction you look from, whereas this device would give you something more like a TV screen, with the same image from any angle. Furthermore, unless you had some sort of lenses or other optical elements on the other side of your high-tech window, there wouldn’t be much of an image in the first place. You’d basically just see the shape of any shadows which happen to fall on your screen.

I’m not sure what you mean about it generating power from thin air. If there’s ambient light, it’ll produce power from that, but that would just mean that you’d need brighter lights in your room. If your device is highly efficient, it’ll look black, and there’s a reason you so seldom see rooms with black walls. Well, OK, seldom outside of a frat house.

3

To answer part of your question, LED’s can be reversed biased to render them into photodetectors. It was the principal I used to design an advanced laser copier in 1971. Usually, photoemitters do not perform as well as photodetectors and vice versa.

The object you seem to be describing sounds like a variable selective optical imaging filter. Whereby you could impose an image onto a photosensitive array (that you also desire to be photovoltaic [nearly impossible BTW]) use the detector and display elements to convert and/or select-deselect certain bandwidths of the image’s spectral composition. This is already done with infra-red imaging systems that “upvert” the wavelength of invisible long wave red light into a visible photofrequency. Sadly, it is impossible to impose anything but false coloration onto such a disply because the original infrared signal does not have the spectral bandwidth to contain what we might refer to as “color”.

To create a color imaging detector/display whose own components also allowed for variable configuration bandpass filtration (lowpass, bandpass, highpass, variable Q or comb filtering) of the transfered optical image would be insanely expensive and consume power that mere imaging signals could neither survive nor provide through photovoltaic effect. As mentioned by Chronos such power generation via photoconversion by the imager would literally prohibit retention of the vital color and positional information carried by the arriving lightwaves.

What I think you might be hoping for here is a compact self-powered monolithic combination imager and viewscreen that could optically sort and selectivly transmit (or pass) color specific protions of an image to the display. Therefore, you might be able to sort out all of the red items in an image looking for a wounded soldier on a crowded battlefield or isolate a flesh tone in a jungle picture to find a sniper. Is this somewhat close to your application?
If not, feel free to disregard the entire preceeding post.
(Mind you that this is already done by color video image subtraction and sorting systems. They just happen to require so much power that you would have to cover your body in a flexible suit of organic photovoltaic arrays and stand in bright sunlight just to operate it.)

4

Light hitting photo-transistors does not produce anywhere near the amount of voltage that is useful, except in the manner that they are used: they are already biased, and the small light that hits the base of the transistor (not meaning bottom, but base from collector emitter) and allows it to conduct.

I don’t know much about photovoltaic cells though, sorry.

I had learned in school that all transistors would respond to light, which is hwy they are cased in black plastic. Kind of hard to test that out myself, so I’ve been stuck on someone’s word.

5

Guys, this is very very much exactly the sort of information I was looking for. It will be incredibly useful to me. Thank you again.

I will see if I can’t put up some very basic schematics later in the day. I admit I know next to nothing about this stuff, but I’d like to see what you have to say about a design I’ve been kicking around.

If anyone has any information on the non-visible spectrum laser question asked in the last few paragraphs, I’d appreciate your input, also.

Thank you everyone.

–Tim

6

I have drawings and very, very basic schematics, but I can’t post images or even scan them in, so bear with me.

I realize what I’m going to quote is non-scientific, and mayhap not even possible. I also understand that I do not know what I am doing, so bear with me if I make basic errors or suggest the impossible - but remember, the merely hard we do immediately, the impossible just takes time, to paraphrase the motto of the Army Corps of Engineers.

A good part of this was written before receiving the information above and has not been revised since, so forgive errors below which were fixed beforehand by Zenster, Chronos, or erislover.

I hope that makes sense to all of you.

Zenster: That is actually an application that I had not previously imagined, but would actually be a very neat trick. Perhaps something like that would be easier to produce if we used a selectively light permeable film that, when tuned to a certain electrical frequency, only allows the passage of certain light frequencies - think a derivative of current light-sensitive window tints. That would do away with most of the power needs, I would think, and really cut down on the complexity of the necessary components.

Chronos: As for the image being static, that’s okay, I was really looking for a way to make a monitor or TV screen be able to trickle-charge it’s battery or power supply while non-active. The fun thing is, the bigger the display, (think movie screen) the more power it would accumulate. For instance, a drive-in theater with such an array could absorb energy throughout the day to power the screen for the duration of a movie that night.

–Tim

7

Does anyone have any further comments or insights on the topic?

–Tim