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According to this guy it is feasible to use LEDs to detect light, because they will turn any light emitted on them into a tiny voltage that can be used in a sensor.

Since modern flat screens (OLD) found in some mobile phones and TV sets are basically just big arrays of organically grown LEDs, would it be feasible to produce power from light when they are switched off, effectively turning them into solar panels?

EDIT: I clarified the question to mean OLED based displays. Backlit displays is not what I had in mind.

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  • \$\begingroup\$ "Since modern flat screens such as TV sets and PC monitor are basically just big arrays of LEDs, " Wow. No. \$\endgroup\$ – Ignacio Vazquez-Abrams May 27 '15 at 19:27
  • \$\begingroup\$ Well arn't OLED just organically grown LEDs on a matrix? I am no expert, that is why I ask. \$\endgroup\$ – Lennart Rolland May 27 '15 at 19:28
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    \$\begingroup\$ Most flat screen devices are LCD panels that use either a CCFL or LED backlight. But large OLED panels are not economical yet regardless. \$\endgroup\$ – Ignacio Vazquez-Abrams May 27 '15 at 19:29
  • \$\begingroup\$ I updated the question. I put OLED in title and tag but now I also mention it in the text. \$\endgroup\$ – Lennart Rolland May 27 '15 at 19:32
  • \$\begingroup\$ As Asmyldof explained, to use an OLED display for energy harvesting is not practical. But imagine if you have a pen which output a light beam instead of ink, use this pen to write on the display, we can make a display into a very precise touch screen. Because every pixel is registered inside, the precision can be pixel level high. \$\endgroup\$ – Zone Thin May 17 '17 at 7:26
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As Ignacio points out in the comments:

Most large screens (if not all) are LCD types, usually either TN (Twisted Nmatic) or IPS (In Plane Switching), with a certain type of backlight. "LED TV" just means they are using LEDs to shine on the back of the display. Some more expensive ones might use 16 different sections, or even more with independently controlled LEDs, to give you the experience of more range in the brightness. In other words, faking the static contract ratio, by having one section that contains a lot of black dim the LED, and another that is very bright turn it all the way up.

But that's about the level of sophistication in the LEDs that "drive" the main picture. OLEDs are expensive and take a lot of time to make, whereas LCD is a piece of cake. Remember several Mobile phone brands making an OLED model around 2012-ish and then quickly announcing they'd also start using normal LCDs due to sourcing issues? I do!

To answer your actual question, assuming there is an LED-Pixel TV, with say 4K resolution. That's 8.29 million LEDs with each an R, G and B.

((I'd guesstimate its price tag somewhere in the $ 50000+ range))

And then a LED of that microscopic size will have never have the same effect/performance as a normal size LED that they put in a 3mm housing.

So, what does a LED do when light falls on it? It tries to induce a current, because some of the photons hit the substrate such that electrons get annoyed in one general direction, much like in a photo-diode. (<-- concise slang for a whole lot of techno gibber about valence, energy states, recombination, reverse action, transport, electrons and electron gaps)

That's like in a Solar cell! Yes, exactly, but also no. The difference is in the magnitude of the effect. In a Solar Cell huge amounts of electrons get buggered into moving, seriously, busloads of busloads. That's partly because of their structure, but also because of their giant surface compared to a measly diode. In a photo diode, it'll be one or more orders of magnitude less per unit surface area, because they are still engineered to do that, but also to be as linear as possible, this is sort of a trade-off. Solar cells are efficient, but far from linear in their response.

In a LED the materials are composed and ordered such that as many electrons flowing cause photons to be generated as possible (what else would you engineer it for?). Unfortunately this isn't the way to go if you want to generate energy. A LED will only induce a few micro ampere when you shine a light on it. And that even also depends on its colour. A Red LED can't see blue very well, for example.

So, even if we assume a microscopic Organically grown LED can induce 1uA and reach 0.1V (I think this would still be very generous) while that current flows, a TV with 8.29 million sets of three LEDs would only reach 8.29 * 10^6 * 3 * (1 * 10^-6)A * 0.1V = (8.29 * 3 * 0.1)W = 2.49W

Would you engineer the electronics to capture that into a TV that already cost you way too much in OLED materials? Let alone, mount your personal TV in direct light for that? It'll basically mean that if you mount your TV in the sunlight, it might be able to stay on stand-by for free. Might be able to.

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  • \$\begingroup\$ Not to mention the adverse effect of direct sunlight on plastic, which will reduce the lifetime of the expensive OLED matrix. \$\endgroup\$ – Dmitry Grigoryev May 27 '15 at 22:18
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    \$\begingroup\$ @DmitryGrigoryev Ah, piece of gorilla glass and some high grade low-ageing fibre materials won't increase the bill that much. \$\endgroup\$ – Asmyldof May 27 '15 at 22:26
  • \$\begingroup\$ What kind of "high-grade low-ageing fibre materials" can emit light and be used in OLEDs? \$\endgroup\$ – Dmitry Grigoryev May 27 '15 at 23:01
  • \$\begingroup\$ @DmitryGrigoryev I foolishly only registered 75% of your comment and inferred the plastics in the TV itself, not even considering the substrate used to grow the LED matrix onto. \$\endgroup\$ – Asmyldof May 27 '15 at 23:14
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Modern OLED use PEDOT used as a organic transparent substance in nature

This substance don't show any photo-conductivity,though they are conducting,and anode and cathode are being applied cross them hence electron flow through them,they are called the substrate of the OLED display.


These layer are then coated with Rubrene and Rhodamine which are responsible for the electroluminescence,which is made more effective later by using fluroluminescence.

These display then are breaked in matrix called pixels by various method with TFT or any other technology and each pixels are addresed using data line matrix.OLED are mostly flexible and transparent though they need a reflective layer on back to increase illumination.

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