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The retina is light sensor, which converts light to an electrical signal. LEDs can both emit and receive light. Similarly, is it possible to apply electricity to retina to generate light?

Simply put, in theory, can humans emit electromagnetic waves from their eyes?

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    $\begingroup$ @user137 but The main point is I want to know mecanic of absorption and energy conversion of retina that is it the same as LED or not. If it is then we could grow organic LED with bioengineering $\endgroup$ – Thaina Jan 6 '16 at 7:01
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    $\begingroup$ Close voter and skeptics: this is a great question. Ever heard of otoacoustic emissions? Ever thought about the physics between photon absorption and relaxation generating fluorescence? $\endgroup$ – AliceD Jan 6 '16 at 7:54
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    $\begingroup$ It is very interesting but it's making no attempt to understand the biology of the problem, I'm going to close vote but would retract/reopen if the user makes it more biologically focused. $\endgroup$ – rg255 Jan 6 '16 at 8:03
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    $\begingroup$ I'm voting to close this question as off-topic because it needs to explicity seek understanding of the biological considerations. $\endgroup$ – rg255 Jan 6 '16 at 8:04
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    $\begingroup$ @user137 - first you guess any photo emittance would swamp the retina and then you guess the efficiency would be too low to occur anyway? Criticizing questions is OK, shooting at them randomly with unfounded arguments is not. $\endgroup$ – AliceD Jan 6 '16 at 11:24
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Please allow me to start by saying I know nothing about LEDs, so my answer isn't going to address your analogy. I'm also going to keep it more simple.

Can the retina emit light?

Yes. The retina is able to give off light in the form of fluorescence. Since fluorescence is the emission of light by a substance (granted that substance must first absorbed light or other electromagnetic radiation of a different wavelength.)

“We can use autofluorescence emission to image the retina and see certain features of it,” said Dr. Sparrow, the Anthony Donn Professor of Ophthalmic Science in the departments of Ophthalmology, and Pathology & Cell Biology. ...Most objects in the environment are visible because they reflect, as opposed to emit, light. However, the retina—which exists within the eye’s back wall, known as the fundus—can generate its own fluorescence.

The cells of the deepest layer of the retina, called the retinal pigment epithelium (RPE), contain fluorescent compounds, which when excited by blue light emit a yellow fluorescence.

This ability changes with age, disease, etc.

Excessive accumulation of lipofuscin granules in the lysosomal compartment of retinal pigment epithelium cells represents a common downstream pathogenetic pathway in various hereditary and complex retinal diseases, including age-related macular degeneration.

Lipofuscin is one of several fluorophores in the RPE. Different fluorophores may be related to different damage to the eye.

A major hydrophobic component of RPE lipofuscin is the fluorophore A2E... Given that A2E strongly absorbs in the blue region of the spectrum, together with the known susceptibility of RPE to blue light damage, we undertook to investigate A2E as a fluorophore involved in blue light toxicity.

Science Insight: Using the Retina’s Natural Fluorescent Light to Measure and Treat Disease
FUNDUS AUTOFLUORESCENCE IMAGING: Review and Perspectives
The Lipofuscin Fluorophore A2E Mediates Blue Light–Induced Damage to Retinal Pigmented Epithelial Cells

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  • $\begingroup$ Thanks for your answer. But the main point I mention LED is because it is photovoltaic, conversion between electricity and electromagnetic wave. The point is photovoltaic will absorb wave to generate electric current. And it is reversible material that if apply electric current it will emit light. So I wonder if the mechanic of light absorbtion to convert light energy to electric signal of retina is photovoltaic then it could reversible by retina material emit light when apply cirrent $\endgroup$ – Thaina Jan 7 '16 at 1:11
  • $\begingroup$ Still your answer amaze me that retina is also fluorescence emitting yellow light. So maybe human always see blue light with a bit of yellow, never see true blue, or even any true color if other cell fluorescing other light too $\endgroup$ – Thaina Jan 7 '16 at 1:19
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    $\begingroup$ @Thaina To specifically address the idea of using electricity to make photoreceptors "work in reverse" and emit light, we have to look at how photoreceptors work. A photon hits a chemical in the receptor, causing it to absorb energy and change shape. This triggers a series of proteins to signal each other and eventually close sodium and calcium channels. With those channels closed, the cell becomes hyperpolarized. While this is described in terms of electric charge, it is not the same as semiconductors like LEDs. $\endgroup$ – user137 Jan 7 '16 at 5:28
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I think is an simple yet very applicable answer here.

Anything with a temperature will emit photons via thermal radiation.

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