17 votes

If eyes emitted light, could they still see?

Ok, this is one of those thoughts I have in my brain and that I can't quite get rid of.
It breaks down into a couple of questions. For the purposes of this, I'm aware that what eyes see is the reflection of light bouncing off objects, but I'm curious the impact on the visibility of both objects and other lights.

A. If eyes emitted any light, could they still see anything at all?
B. If eyes emitted, for example, red light, could they see everything except red items? What about red lights? Does this change if the light is green or violet?
B.1. If they can't red things would they just be invisible?
B.2. If they can't see red lights, would it matter if the red light they're seeing is brighter or dimmer, and would it still be an invisible/blank space?
C. I'm not sure how infrared interacts here but I know animals that sense infrared do emit it, is there a reason that's different, if it's different.

The internet is mostly not super helpful with this, since eyes don't emit light, just reflect it and look glowy, but yeah, anyway... thanks for entertaining my weird fixation.

36 comments

  1. [9]
    stu2b50
    Link
    If the light source in the eyes is fairly scattered, it would make it hard to see, depending on the intensity of light. That's because a lot of the light the eyes would detect would just be coming...

    If the light source in the eyes is fairly scattered, it would make it hard to see, depending on the intensity of light. That's because a lot of the light the eyes would detect would just be coming from the eyes itself, so a lot of noise and not a lot of signal.

    If it were focused, like a laser, then you'd see perfectly fine. You'd just have built in flashlights. It's not very different than cameras with built in flashes.

    If that light were skewed to a particular wavelength, then it would be as if you have a red flashlight. Things within that cone (or cylinder, if it's not angled) would look red-er. That's about it.

    17 votes
    1. [6]
      arch
      Link Parent
      Well, I believe camera flashes work by first emitting the flash, then a short (pretty much imperceptible to us) delay later taking the picture.

      It's not very different than cameras with built in flashes.

      Well, I believe camera flashes work by first emitting the flash, then a short (pretty much imperceptible to us) delay later taking the picture.

      6 votes
      1. [5]
        sth
        Link Parent
        What use would the flash have if you take the picture after it's already over? You want the picture to capture the light from the flash, so you have to take it during the flash. For all practical...

        What use would the flash have if you take the picture after it's already over? You want the picture to capture the light from the flash, so you have to take it during the flash. For all practical purposes the scene immediately goes dark after the flash is over, since the speed of light is extremely high.

        1 vote
        1. [4]
          arch
          Link Parent
          I started looking into it, and honestly camera shutter timing, flash length, and the speed of light are way more complicated than I can even begin to understand. The thought I had was that you...

          I started looking into it, and honestly camera shutter timing, flash length, and the speed of light are way more complicated than I can even begin to understand. The thought I had was that you need to capture the light bounced off your subject, but too bright of light at the bulb would risk washing out your exposure, so time the shutter imperceptibly after the flash. But after trying to research it I can't find any corroborating sources that this is actually what happens.

          1 vote
          1. PetitPrince
            (edited )
            Link Parent
            I've done and taught studio photography, here's how I understand this: As you said, the quantity of light you gather in your sensor is critical. Too much and your picture is too bright, too little...
            • Exemplary

            I've done and taught studio photography, here's how I understand this:

            As you said, the quantity of light you gather in your sensor is critical. Too much and your picture is too bright, too little and your picture is all black. One important factor to take into account is the exposure time, which is the time the sensor is exposed to the scene.

            Normally the scene is lit with "ambient" light. It can be the sun or an existing light fixture or whatever. They're continuous source of light. A flash is a punctual source of light. For the purpose of photography, it has no duration. The shape, power and direction of the light is important. You typically want something that looks plausible so that if feel pleasant to the eye (typically a light coming from the floor looks really unnatural). There's also some technical limitations (it's hard and/or expensive to out-compete the sun in term of light produced, but see the spoiler at the bottom for a technical workaround).

            So what's happening when photographing with a flash ?

            Here's a graph:

                                         1    2         3         4    5   
            Shutter                     ----[[[[[---------------]]]]]-----> 
            A. Flash (front curtain)    ----------X-----------------------> 
            B. Flash (rear curtain)     -----------------------x----------> 
            C .Flash (stroboscopic)     ----------x---x---x---x-----------> 
            

            The common sequence of things is as follows:

            1. The sensor is not exposed
            2. The shutter opens [[[[[
            3. The sensor is exposed
            4. The shutter closes ]]]]]
            5. The sensor is no longer exposed

            The sensor will capture ambient light whenever the sensor is exposed, and putting a flash will add additional light on top of it.

            As long as the flash fires when the sensor is exposed, the final image will have this additional light in it.

            A. The default mode of operation is to time the flash is to fire the flash just after the shutter opens (this is called "front curtain", more on that later).

            B. However if you have a relatively long exposure time, you can play with the timing of the flash and time the flash so that if happens just before the shutter closes. You do this to have some tasteful trails, most of the time to put an emphasis on movement. Stuff like this.

            C. You can also do YOLO and fire your flash at regular interval (typically with a very long exposure time) to get a stroboscopic effect (a stroboscope is a mechanical device with a rotating part and a continuous light; most consumer flash can just fire in a quick succession). This is a rather extreme example. Here you put emphasis on movement by having multiple picture in the one.

            It's easier to have such effects when the ambient light is low enough so that the background cannot be captured by the sensor. With long exposure time, any ambient light will make a trail out of any movement, and you want to control that. However with a flash, you kind of freeze a moment in time.

            Outside of the studio, having a slow shutter speed have the risk of having a background that's blurry because of the movement of the camera (as opposed to an out-of-focus blur). In this picture the photographer set an exposure time long enough to have a trail for a rear curtain flash, but you can see that the background is rather smudgy.

            It's always a challenge to balance exposure (how much light you have), blur (intentional or not), and technical limitation (you can have more light gathering power by buying more expensive sensor and/or objectives, but you may not have the budget and/or the will to carry heavier equipment).

            Recent development for photography nerds

            A relatively recent development is the so-called "high speed sync". The mechanics of a shutter make it so that the opening and closing action of a shutter takes a times (notice that in the graph those event are not only 1 symbol), and that with very short exposure time (typically faster than 1/250th of a second), the closing action begins before the opening action has time to finish. See the "rolling shutter" artifact for more info. So if you take have one flash, only a sliver of your picture will receive the light (this happens).

            With high speed sync you effectively put multiple low power flash in one exposure. In diagram form it looks like this

            Shutter (high speed sync) ----[[[////]]]------>
            Flash (high speed sync)   -----x---x---x------>
            

            But this image is more informative than my ASCII diagram.

            With HSS you can do picture like this where you can outcompete the sun without resorting to huge and heavy lights. You do that by reducing the firehose that is the sun to a little squirt by having an extremely short exposure time (in this picture, 1/8000 sec.), and then you bring you own light (note that an alternate way to get the same effect would be to bring a reflector and effectively have a secondary continuous source of light, but sometime you want a different quality of light and/or the reflector has no handy source of light to bounce )

            5 votes
          2. teaearlgraycold
            Link Parent
            It should be easy enough to design the camera such that the flash doesn’t enter the lens directly.

            It should be easy enough to design the camera such that the flash doesn’t enter the lens directly.

            2 votes
          3. sth
            Link Parent
            If you are photographing something 15 meters away, the light from the flash takes 1/10,000,000 of a second to get there and back again. So that's the time you still see light after the flash...

            If you are photographing something 15 meters away, the light from the flash takes 1/10,000,000 of a second to get there and back again. So that's the time you still see light after the flash turned off. Typical shutter speeds are 1/1,000 of a second or slower. This is 10,000 times as long at the "residual flash". Clearly this doesn't really add up if you want to just capture that ten-millionth of a second with residual flash.

            The trick is to not let the flash shine into the lens directly, usually by positioning it appropriately. The light form the flash can't get into the lens directly, so it doesn't disturb the picture. It's the same as putting up big lights at a movie set. The lights are always on during filming, but they are behind the camera or to the side so they don't shine into the camera directly.

            2 votes
    2. [2]
      vektor
      Link Parent
      I'm wondering if this is even physically possible. A lot of things in optics are perfectly symmetrical backwards and forwards. So if you had an optical device that focused light forwards, then any...

      If it were focused, like a laser, then you'd see perfectly fine.

      I'm wondering if this is even physically possible. A lot of things in optics are perfectly symmetrical backwards and forwards. So if you had an optical device that focused light forwards, then any light coming in would be focused into the light source, and couldn't end up in the receptor cells.

      If you were to intersperse at the retina layer:

      • light sources in parabolic mirrors
      • and all the usual retinal cells

      Then you might end up in the awkward spot where the light sources project to exactly those spots in the image (image here being the outside world before your eyes) where your retina has no reception. Meaning you yourself couldn't see any of the light, because the lights are tiny spots in your FoV, and you happen to have blind spots in each of those spots.

      Then again, if the lens in your eye is just a little imperfect, you'd get a bit of a blur: The outgoing light is blurred a bit, as well as the incoming light. If the blind spots are smaller than the blur, they'd be unnoticable and it'd work.

      Even if it's very high efficiency LEDs though, the waste heat would probably burn your retina.

      1 vote
      1. TangibleLight
        (edited )
        Link Parent
        That's an interesting point! You would still see interreflections and caustics and other things. Think in terms of global illumination from computer graphics. But if you were to look at a blank...

        Then you might end up in the awkward spot where the light sources project to exactly those spots in the image (image here being the outside world before your eyes) where your retina has no reception.

        That's an interesting point! You would still see interreflections and caustics and other things. Think in terms of global illumination from computer graphics. But if you were to look at a blank wall in a dark room, I think yes, all the direct reflections would fall back nearly onto the light sources on the retina.

        The easy solution is to bring the light sources up out of the focal plane. This is how reflector telescopes can produce a clear image even though there is an object - the secondary mirror - obstructing the view. It's not in the focal plane so that obstruction gets "blurred" across the entire image and doesn't really impair visibility other than reducing the total brightness of the image.

        So you could imagine a setup where you had a reflector telescope, and next to the secondary mirror you also had a flashlight shining out. That light would reflect off the environment and back into the telescope. The flashlight and the secondary mirror would cast a shadow on the detector, but they're so far out of focus they wouldn't impede visibility.

        The equivalent in the eye would be a focused light suspended somewhere in the middle of the eye, shining out of the eye but not back into it. You could construct it like a source off to the side, shining perpendicular to the line of sight, and a little mirror at 45° suspended in the middle of the eye that reflects that light outward. It would obstruct some of the incoming light, but would be so blurred that you should still be able to see details. Or maybe something with optical fiber?

        1 vote
  2. [6]
    TangibleLight
    (edited )
    Link
    I'm not sure the question is quite well-formed enough to give a satisfying answer. I think the most correct answer is: if they can see while they emit the light then yes; if they can't see while...

    I'm not sure the question is quite well-formed enough to give a satisfying answer. I think the most correct answer is: if they can see while they emit the light then yes; if they can't see while they emit the light then no. It all depends on how the fictional mechanism works so, being fiction, it's totally up to how you choose to ask the question.

    A couple facts that might clarify things:

    • Light can travel multiple directions in the same space, and they don't affect each other. Just as light can travel both ways through a window, light can travel both ways through your eye. Your eye can still receive light even if it's emitting it.

      • Unless the fictional mechanism that emits light also made the eye opaque, or disabled the retinal cells.
    • Multiple colors of light can pass through the same space, and they don't affect each other. So even if your eye emits red light, it can still receive blue light.

      • Unless the fictional mechanism that emits red light also made the eye opaque to blue light, or disabled the blue cone cells.
    • An object that emits no light isn't perceived as invisible; it is perceived as black. An object that emits no red light but does emit blue light is perceived as blue. Nothing in your scenario would make things suddenly appear "invisible," that is, transparent.

    • Simplifying a lot (because I lack expertise for a real explanation), your retinal cells have a limited ability to be "on" and can be overwhelmed. This is why you see dark spots in your vision if you stare at a light for some time: the retinal cells get tired and need to wait a bit before that color can be "on" again.

      • So, if the fictional device that emits light also activated your retinal cells, then it might saturate your vision and you wouldn't be able to see. However if the light were situated in a way that it did not activate your retinal cells, or if your retinal cells were somehow adapted to the extra light, then you'd still be able to see.
    • On infrared: everything emits infrared light by virtue of its temperature. In all cases, the object can still absorb and reflect and transmit light that's cast onto it. Red hot glass is still transparent. Red hot steel still looks brighter if you shine a light on it. Things are no different with infrared.

      • You can perceive infrared light, too, go stand out in the sun. You feel the warmth from it even though you're emitting your own infrared light at the same time.
      • So, again, it depends on the construction of the fictional mechanism. If it's such that it can receive infrared light at the same time it emits it, then it can see fine.
    12 votes
    1. [2]
      DefinitelyNotAFae
      Link Parent
      Hm thank you for that so yeah, I was somehow thinking particularly of things in the dark but absolutely didn't mention it because I had so many random thoughts. Sorry the question wasn't...

      Hm thank you for that so yeah, I was somehow thinking particularly of things in the dark but absolutely didn't mention it because I had so many random thoughts. Sorry the question wasn't formulated sufficiently.

      This definitely didn't come from me driving on a particularly dark night and seeing the wind farm lights flash and creating a whole world in my head (⁠;⁠;⁠;⁠・⁠_⁠・⁠)

      So if red light comes out of the eye, red light could still get in.
      If the retina was overwhelmed by the red light, and that was the only light available, it doesn't sound like they'd see very well.

      So if my wind farms are giant alien monsters, escaping them by using red lights would probably be behavioral, not physics. 🤔

      6 votes
      1. TangibleLight
        (edited )
        Link Parent
        Yeah, if you just embedded a little red LED in the center of your eyeball (ouch!) it would shine in all directions. It would shine out, but also shine directly onto your retina. It would overwhelm...

        Yeah, if you just embedded a little red LED in the center of your eyeball (ouch!) it would shine in all directions. It would shine out, but also shine directly onto your retina. It would overwhelm your retinal cells and you likely wouldn't be able to see much of anything, same as if an oncoming car had very bright red headlights and washes out your vision.

        But if you had some lasers-and-mirrors contraption in there so the light shone out your eye but not back onto your retina, then you'd probably be able to see fine.

        Note there is a heat component, though, if you want a light as bright as your car's headlights, it's also gonna also be as hot as your car's headlights. I don't know if you've ever touched your eye to your car's headlights after a long drive - it's very hot, I don't recommend it.

        But if you're out in the dark a long time and let your eyes acclimate to the low light, you could probably get away with a fairly dim lantern-brightness light that would not be so hot.

        Before you go implanting red lights in your eyeballs, I might recommend one of these instead. I expect the benefit to be comparable.

        So if my wind farms are giant alien monsters, escaping them by using red lights would probably be behavioral, not physics.

        As a rule of thumb: if you can see the signal, so can your attacker. There is "active sensing", where you have a flashlight and observe the reflections, or you send a ping and wait for echoes. Any active sensing just serves as a beacon to your location. Think how far away you could see someone who is carrying a flashlight in a dark forest.

        There is also "passive sensing," where you just wait and listen, think of nightvision goggles amplifying infrared light, or cats with the "glowy eyes" - the glow is a reflective layer in their retina that amplifies dim light. Passive sensing is by far the stealthier option.

        So yes, escaping by red flashlight - embedded in your eyes or not - is probably behavioral. Escaping by dim starlight or by passive infrared sensing is probably physics.

        8 votes
    2. vektor
      Link Parent
      Far as I know, mechanistically, this happens because the retinal cells produce photosensitive compounds, and those are available in limited quantities at any given time, and their production rate...

      Simplifying a lot (because I lack expertise for a real explanation), your retinal cells have a limited ability to be "on" and can be overwhelmed.

      Far as I know, mechanistically, this happens because the retinal cells produce photosensitive compounds, and those are available in limited quantities at any given time, and their production rate is also limited. So if you look at a bright thing, you're burning through the available supply faster than it can be replenished, and now your retinal cells are much less sensitive than they otherwise would be.

      BTW, this effect can make for very fun sensations when one of your eyes has been "burnt out" more than the other. I've had that happen when an eye patch was taken off. The patched eye had incredibly vivid colors, and it kinda messed with my brain, trying to reconcile the two images.

      2 votes
    3. [2]
      sparksbet
      Link Parent
      This is a bit of a nitpick, but you mean objects that neither emit nor reflect light, right?

      An object that emits no light isn't perceived as invisible; it is perceived as black. An object that emits no red light but does emit blue light is perceived as blue. Nothing in your scenario would make things suddenly appear "invisible," that is, transparent.

      This is a bit of a nitpick, but you mean objects that neither emit nor reflect light, right?

      1. TangibleLight
        Link Parent
        Sure, that's fair. I was using it in a looser sense of "to cause the eye to receive light". The point was more that "emitting light" (in this vague sense) and "being visible" are not the same...

        Sure, that's fair. I was using it in a looser sense of "to cause the eye to receive light". The point was more that "emitting light" (in this vague sense) and "being visible" are not the same thing.

        And really, transparency is not even the right quality. Glass and water are transparent, but even without reflections they are still visible because of how they refract and scatter and absorb the background light that passes through them.

  3. [2]
    RoyalHenOil
    Link
    In principle, I don't see why this couldn't work. After all, our bodies emit heat, yet we can still perceive heat from other sources. The brain accounts for ambient temperature (including our own...

    In principle, I don't see why this couldn't work. After all, our bodies emit heat, yet we can still perceive heat from other sources. The brain accounts for ambient temperature (including our own body temperature) in order to pick signals out of the noise.

    There are a number of deep sea fish that emit light directly from their eyes or from bioluminescent organs directly adjacent to their eyes. In many of these cases, it appears the fish have effectively evolved bioluminescent flashlights: that is, they emit light in order to see what bounces back.

    8 votes
    1. DefinitelyNotAFae
      Link Parent
      This makes sense. I was definitely thinking of how some of the ways that rods and cones get exhausted I think in contrast with heat and that eyes can't pick up all wavelengths. If my glowing eyes...

      This makes sense. I was definitely thinking of how some of the ways that rods and cones get exhausted I think in contrast with heat and that eyes can't pick up all wavelengths. If my glowing eyes couldn't see red light though their glowy eyes wouldn't let them hunt humans in the dark.

      I am not testing the design of new Wild Hunt hounds.

      But I'm not not testing that either.

      2 votes
  4. [2]
    TonesTones
    Link
    My only qualifications are that I took a waves class in undergrad, but I kinda want to guess what would happen regardless. I’m assuming the eyes are magically projecting light (photons) outwards....

    My only qualifications are that I took a waves class in undergrad, but I kinda want to guess what would happen regardless.

    I’m assuming the eyes are magically projecting light (photons) outwards. So, the only effect on the photons absorbed by the eyes is their interactions with the emitted photons.
    The wavelength (and therefore color) of the photons is determined by their energy. I don’t know much quantum or wave/particle duality, but I assume all photons have the same amplitude (they all travel at the speed of light, where would the extra energy come from if the wavelength is fixed?).

    A. I think so, if the light emitted is fairly dim? My guess is that there would be few enough emitted photons that the incoming photons wouldn’t be impacted much.
    I did my best to test this by putting a flashlight just underneath my eye. Everything has a glare to it, but it’s just kinda more bright than before.

    If your eyes emitted enough photons to collide and interfere with the incoming photons, things would be different. But I suspect the density of photons would need to be high (and therefore the light bright) for this to actually play a role.

    B. My instinct tells me the color would just change the glow of everything, like using ambient lighting. I don’t think photons work the same as standard waves in terms of interference and destruction.
    If you shine a red light at a strawberry, it isn’t as if the red on the strawberry becomes less strong, it just becomes less red as your eyes adjust to seeing all the red photons.

    C. Infared is just another wavelength. We still wouldn’t be able to see it, and animals that do see it would just interact with it like another color under my assumptions.

    Again, I’m assuming the eyes are somehow magically emitting light only outwards. That allowed me to get pretty close to experimenting by putting (dim) flashlights very close to my eye. Sources of light don’t tend to choose in which direction they emit, which means your eyes would be constantly receiving that light as well, and I don’t know how that would change things (except that your eyes would surely get quite hot).

    I’m probably wrong; I am not a physicist. Still, I wanted to think through it from the first principles I am aware of.

    3 votes
    1. DefinitelyNotAFae
      Link Parent
      Appreciate this! Thanks, maybe my magic eyes could be thwarted by the exact correct brightness/hue but it seems unlikely!

      Appreciate this! Thanks, maybe my magic eyes could be thwarted by the exact correct brightness/hue but it seems unlikely!

      2 votes
  5. [3]
    norb
    Link
    Your post made me think of that scene in Ghostbusters 2 where the guy leaves Dana's apartment after checking on her and his eyes light up like flashlights. Interesting question and great comments,...

    Your post made me think of that scene in Ghostbusters 2 where the guy leaves Dana's apartment after checking on her and his eyes light up like flashlights.

    Interesting question and great comments, sorry for the low-effort post on my part.

    3 votes
    1. DefinitelyNotAFae
      Link Parent
      Nah this was not a high effort question!

      Nah this was not a high effort question!

      2 votes
    2. ChingShih
      Link Parent
      This video (imgur) is not at all relevant to the topic at hand, and yet ... (possibly a little creepy).

      This video (imgur) is not at all relevant to the topic at hand, and yet ... (possibly a little creepy).

      2 votes
  6. LumaBop
    Link
    Just to add on to this, because I don’t think I’ve seen this mentioned: Assuming that the source is able to project light in a focused manner out from the eye (as in @stu2b50 ‘s laser/flashlight...

    Just to add on to this, because I don’t think I’ve seen this mentioned:
    Assuming that the source is able to project light in a focused manner out from the eye (as in @stu2b50 ‘s laser/flashlight example), I believe the main problem you would have is that you would have a hard time using a mirror (because it would be like staring into a flashlight), and might not even be able to look through windows/glass for a similar reason, since most glass or transparent plastics are fairly reflective. It would be similar to when you look out a window at night with a light on inside your room - you mostly just see your reflection. The reflection of the light source in your eyes could be stronger than the light from the other side of the window.

    2 votes
  7. [6]
    kingofsnake
    Link
    I didn't run a search but upon scanning, I'm disappointed that I didn't even see one comment about the XMan Cyclops and his magic sunglasses.

    I didn't run a search but upon scanning, I'm disappointed that I didn't even see one comment about the XMan Cyclops and his magic sunglasses.

    1 vote
    1. [5]
      DefinitelyNotAFae
      Link Parent
      Ok but that's not just light, that's a portal to the force dimension.... Unless it's changed recently! But that honestly makes whether he can see a complicated question... If your eyes are...

      Ok but that's not just light, that's a portal to the punch force dimension.... Unless it's changed recently!

      But that honestly makes whether he can see a complicated question... If your eyes are portals, there's gotta be an issue with your retina's ability to even get light.

      1 vote
      1. [4]
        kingofsnake
        Link Parent
        Force dimension must be some deep comic explanation that I skipped over thanks to my Fox Kids cartoon diet of X-Men. I guess our answer is in the description of how the glasses work. Reflective...

        Force dimension must be some deep comic explanation that I skipped over thanks to my Fox Kids cartoon diet of X-Men.

        I guess our answer is in the description of how the glasses work.

        Reflective inner lenses that project the force dimension back in on itself where, some little gnome deduces dictates what it sees to Cyclops' earpiece?

        I'll never look it up so I'll never know.

        1 vote
        1. [3]
          DefinitelyNotAFae
          Link Parent
          I have no idea how or why I know about the force dimension. But gnomes are the best possible answer

          I have no idea how or why I know about the force dimension. But gnomes are the best possible answer

          1 vote
          1. [2]
            kingofsnake
            Link Parent
            Gnomes with mirrors behind your own sunglasses perhaps? Maybe the reason for starting a thread about such a topic? 😉

            Gnomes with mirrors behind your own sunglasses perhaps? Maybe the reason for starting a thread about such a topic? 😉

            1. DefinitelyNotAFae
              Link Parent
              Once again, sylvan and fae folk of all sorts are explicitly not my area of expertise, the username should make that absolutely clear, but it does seem to cause confusion. ༄˖°.🍂.ೃ࿔*:・

              Once again, sylvan and fae folk of all sorts are explicitly not my area of expertise, the username should make that absolutely clear, but it does seem to cause confusion.

              ༄˖°.🍂.ೃ࿔*:・

              1 vote
  8. [2]
    PetitPrince
    Link
    Cats and dogs and other animals have a structure called tapetum lucidum in the back of their eyes. They're essentially retroreflector (mirror that sends light back to their source), and for some...

    Cats and dogs and other animals have a structure called tapetum lucidum in the back of their eyes. They're essentially retroreflector (mirror that sends light back to their source), and for some pedant interpretation of your question they are light emitter. That's the reason they are slightly creepy at night.

    They see fine and it's a way to improve the signal when in a low light situation.

    1 vote
    1. DefinitelyNotAFae
      Link Parent
      I asked here because all I could find was info related to animals reflecting light, but that wasn't what I was asking, even if reflecting and emitting both involve light exiting the lens

      I asked here because all I could find was info related to animals reflecting light, but that wasn't what I was asking, even if reflecting and emitting both involve light exiting the lens

      1 vote
  9. [2]
    alden
    Link
    Your eyes already do emit light! Quite a lot of light, in fact. Your whole body is constantly glowing with infrared light. It's just at too low a frequency for you to see.

    Your eyes already do emit light! Quite a lot of light, in fact. Your whole body is constantly glowing with infrared light. It's just at too low a frequency for you to see.

    1. DefinitelyNotAFae
      Link Parent
      Sure but since I can't see it, it doesn't help me determine if emitting it prevents seeing it. Or at least it doesn't prove it

      Sure but since I can't see it, it doesn't help me determine if emitting it prevents seeing it. Or at least it doesn't prove it

      2 votes
  10. Raspcoffee
    Link
    Assuming this is visible light, exactly where on the eye is the light emitted? If it's on the outer whiter part of the eye and not directly shining back in the pupil, it could work. It could be...

    Assuming this is visible light, exactly where on the eye is the light emitted? If it's on the outer whiter part of the eye and not directly shining back in the pupil, it could work. It could be like having your flashlight on the smartphone on while filming, depending on intensity, direction etc.. If it's on the inside, it could scatter and, depending on how much light, effectively turn you blind because it'd overwhelm, well, your ability to see.

  11. [2]
    X08
    Link
    we've found the Night Elf!

    we've found the Night Elf!

    1. DefinitelyNotAFae
      Link Parent
      I couldn't possible speak to matters of elves and fairies.

      I couldn't possible speak to matters of elves and fairies.

      1 vote