4 ms·

I'm very curious what the effect would be over the course of decades of having even very weak lasers hitting your retina directly.

by gshdg 7y ago

DangerousPie 7y ago
If the lasers are low-powered enough it should be just the same as looking at a screen, shouldn't it? Either way the same amount of photons are hitting your retina, with a laser they are just aimed more carefully.
- wtdo 7y ago
  I'm mostly in agreement with you, but the part that gives me concern is precisely how precisely the lasers will be aimed at the retina. I doubt anyone ever really looks at a screen in the exact same place (even if you are staring at a specific character) due to eye jitter. After a year or twenty of use are we going to start having burn-in on our retina's similar to plasma screens used as kiosks?
  - asdff 7y ago
    If research shows that this is possible one need only to code in jitter into your iEye app, like the bouncing LG logo on my TV.
- magduf 7y ago
  With lasers, the photons are collimated, so they're all going almost exactly the same direction, instead of just being scattered like with normal light sources. Because of this, it doesn't take that much laser power in your eye for your lens to focus it down to a small patch on your retina and burn holes in it. So you'll need very low-powered lasers for this to be safe. But it certainly should be possible.
- GuB-42 7y ago
  Lasers are effectively point light sources. We usually think of them as perfectly collimated light, but that's just a special case, where the point is at infinity. The consequence of being a point light source is that lenses can refocus the beam, parallel or not, back into a point. Doing so concentrates a lot of energy on a tiny surface. And if that surface is your retina, then that when it becomes dangerous, literally burning a tiny hole into it. It can never happen with, say, a regular light bulb, or even the sun. It the light source is spread out, the image on your retina, or anywhere else, will be spread out, limiting the energy density. This is an indirect consequence of the second law of thermodynamics called the conservation of etendue.
  - asdff 7y ago
    You can go blind looking at the sun or any high powered light source for long enough. If the laser is at a low enough power, then this is no different than looking at any reflected light. The damage is due to the energy density so you just lower the energy.
jerf 7y ago
Photons do not get a special "laser" tag added to them by physics. If it's all in the visual wavelengths and at intensities below what we experience every day (sunlight is really bright, our eyes hide from us the number of orders of magnitude difference between even normal night-time artificial light and sunlight), there's no issue. (However... since I often see this sorta misinterpreted in the wild on the internet, note that is an if-then statement. If the antecedent is false, I make no claim.) The primary safety concern I have would be met by designing the lasers such that if they are overdriven for any reason, they will physically burn out before outputting enough light to be dangerous. Per the classic Therac-25 [1] case study though, that is one safety feature I absolutely want in hardware. There is no amount of software I would accept to implement that. I would also additionally stick some fuses into the system, tuned below the threshold where the power will burn out the laser, along with of course building the whole battery system to not be able to deliver enough power to power the lasers to a dangerous level. However, I really want excess power to physically burn out the lasers. (I wouldn't want to find out the hard way that an EMP of some sort can overdrive the lasers.) For all that I'm laying out safety systems here, I am quite confident that it could be done safely. We trust our lives to much more dangerous systems all the time. I will say that I can't explain to you how you'd audit that safety, though. [1]: https://www.bowdoin.edu/~allen/courses/cs260/readings/therac.pdf https://www.bowdoin.edu/~allen/courses/cs260/readings/therac...
- marcosdumay 7y ago
  > along with of course building the whole battery system to not be able to deliver enough power to power the lasers to a dangerous level That part is not likely. If you concentrate the light over just a few retina cells, dangerous levels are very low.
- moron4hire 7y ago
  I have a lot of experience with lower-power laser diodes. They are extremely easy to burn out by even the slightest extra current.
- pavel_lishin 7y ago
  > Photons do not get a special "laser" tag added to them by physics. True, but we usually get a pretty wide spread of light energies. These are likely going to be very specific frequencies, hitting similar areas over and over. I wonder if the retina can get fatigued of specific frequencies.
moralestapia 7y ago
Like CRT's, plasma's burn in, but you cannot buy a new set of eyes.
- saiya-jin 7y ago
  till you can of course (well maybe not us, but I see it quite realistically for our children, with some perks like taking pictures, better seeing in the dark, maybe infra, zoom)
  - SketchySeaBeast 7y ago
    If the projected technology trends of the past have taught us anything, we can't make assumptions on anything we'll be getting. For all we know it'll be a hundred years and we'll never crack that tech, but boy will we get better cellphones.

I'm very curious what the effect would be over the course of decades of having even very weak lasers hitting your retina directly.

by gshdg 7y ago

I'm very curious what the effect would be over the course of decades of having even very weak lasers hitting your retina directly.

DangerousPie 7y ago

If the lasers are low-powered enough it should be just the same as looking at a screen, shouldn't it? Either way the same amount of photons are hitting your retina, with a laser they are just aimed more carefully.

wtdo 7y ago
I'm mostly in agreement with you, but the part that gives me concern is precisely how precisely the lasers will be aimed at the retina. I doubt anyone ever really looks at a screen in the exact same place (even if you are staring at a specific character) due to eye jitter. After a year or twenty of use are we going to start having burn-in on our retina's similar to plasma screens used as kiosks?
- asdff 7y ago
  If research shows that this is possible one need only to code in jitter into your iEye app, like the bouncing LG logo on my TV.
magduf 7y ago
With lasers, the photons are collimated, so they're all going almost exactly the same direction, instead of just being scattered like with normal light sources. Because of this, it doesn't take that much laser power in your eye for your lens to focus it down to a small patch on your retina and burn holes in it. So you'll need very low-powered lasers for this to be safe. But it certainly should be possible.
GuB-42 7y ago
Lasers are effectively point light sources. We usually think of them as perfectly collimated light, but that's just a special case, where the point is at infinity. The consequence of being a point light source is that lenses can refocus the beam, parallel or not, back into a point. Doing so concentrates a lot of energy on a tiny surface. And if that surface is your retina, then that when it becomes dangerous, literally burning a tiny hole into it. It can never happen with, say, a regular light bulb, or even the sun. It the light source is spread out, the image on your retina, or anywhere else, will be spread out, limiting the energy density. This is an indirect consequence of the second law of thermodynamics called the conservation of etendue.
- asdff 7y ago
  You can go blind looking at the sun or any high powered light source for long enough. If the laser is at a low enough power, then this is no different than looking at any reflected light. The damage is due to the energy density so you just lower the energy.

jerf 7y ago

Photons do not get a special "laser" tag added to them by physics. If it's all in the visual wavelengths and at intensities below what we experience every day (sunlight is really bright, our eyes hide from us the number of orders of magnitude difference between even normal night-time artificial light and sunlight), there's no issue. (However... since I often see this sorta misinterpreted in the wild on the internet, note that is an if-then statement. If the antecedent is false, I make no claim.) The primary safety concern I have would be met by designing the lasers such that if they are overdriven for any reason, they will physically burn out before outputting enough light to be dangerous. Per the classic Therac-25 [1] case study though, that is one safety feature I absolutely want in hardware. There is no amount of software I would accept to implement that. I would also additionally stick some fuses into the system, tuned below the threshold where the power will burn out the laser, along with of course building the whole battery system to not be able to deliver enough power to power the lasers to a dangerous level. However, I really want excess power to physically burn out the lasers. (I wouldn't want to find out the hard way that an EMP of some sort can overdrive the lasers.) For all that I'm laying out safety systems here, I am quite confident that it could be done safely. We trust our lives to much more dangerous systems all the time. I will say that I can't explain to you how you'd audit that safety, though. [1]: https://www.bowdoin.edu/~allen/courses/cs260/readings/therac.pdf https://www.bowdoin.edu/~allen/courses/cs260/readings/therac...

marcosdumay 7y ago
> along with of course building the whole battery system to not be able to deliver enough power to power the lasers to a dangerous level That part is not likely. If you concentrate the light over just a few retina cells, dangerous levels are very low.
moron4hire 7y ago
I have a lot of experience with lower-power laser diodes. They are extremely easy to burn out by even the slightest extra current.
pavel_lishin 7y ago
> Photons do not get a special "laser" tag added to them by physics. True, but we usually get a pretty wide spread of light energies. These are likely going to be very specific frequencies, hitting similar areas over and over. I wonder if the retina can get fatigued of specific frequencies.

moralestapia 7y ago

Like CRT's, plasma's burn in, but you cannot buy a new set of eyes.

saiya-jin 7y ago
till you can of course (well maybe not us, but I see it quite realistically for our children, with some perks like taking pictures, better seeing in the dark, maybe infra, zoom)
- SketchySeaBeast 7y ago
  If the projected technology trends of the past have taught us anything, we can't make assumptions on anything we'll be getting. For all we know it'll be a hundred years and we'll never crack that tech, but boy will we get better cellphones.