4 ms·

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 (

by 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.
- Darkphibre 7y ago
  Indeed! The neurons can get saturated / reduce their signalling as they adapt, but the recovery time is usually quite fast. You can use the effect to generate colors that are actually impossible in the real world (and are only perceived): https://en.wikipedia.org/wiki/Impossible_color https://en.wikipedia.org/wiki/Impossible_color
- jerf 7y ago
  A reasonable question, but I suspect we'd already have some idea if this was the case. There's a lot of artificial light with relatively few, narrow frequencies already in use. I imagine someone, somewhere in some bizarre application would have discovered this as a problem. Since we only see in three color dimensions, it's hard for us to notice day-to-day, but for instance, some fluorescent bulbs are just 5 spikes in particular frequencies. It looks fairly "white" to us, but it's far from normal light. (I am interpreting your comment as being fatigued of/damaged by very specific frequencies in a way that it would not be fatigued/damaged for the same amount of energy spread out over a wider range still within the given cone's sensitivity range.)
  - pavel_lishin 7y ago
    > (I am interpreting your comment as being fatigued of/damaged by very specific frequencies in a way that it would not be fatigued/damaged for the same amount of energy spread out over a wider range still within the given cone's sensitivity range.) Yep, that's my concern. I don't know if anyone's done long-term studies about low-level light of identical wavelength. I mean, on the one hand, people used to be afraid of fast-moving vehicles, convinced that it was impossible for a human body to survive going faster than 40 miles per hour. But on the other hand, people used to strap radium to their faces because they thought it was a cure-all, too.
SkyBelow 7y ago
>Photons do not get a special "laser" tag added to them by physics. I thought they kinda did. By being very similar wavelength and power, compared to normal light which has all sorts of wave lengths and power. This difference can mean certain rods/cones being stressed more than average and not triggering the sort of fatigue that normal light would cause. Perhaps the best example of a similar concept, though not with lasers, is looking at a total solar eclipse right before or after the sun is fully eclipsed. There is a small period of time where extremely bright light makes it into our eyes, but not he frequencies that cause pain normally associated with looking at the sun. This means that our default defenses against looking at the sun don't kick in and doing permanent eye damage is extremely easy without feeling any pain as the damage is done.

by jerf 7y ago

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.

Darkphibre 7y ago
Indeed! The neurons can get saturated / reduce their signalling as they adapt, but the recovery time is usually quite fast. You can use the effect to generate colors that are actually impossible in the real world (and are only perceived): https://en.wikipedia.org/wiki/Impossible_color https://en.wikipedia.org/wiki/Impossible_color
jerf 7y ago
A reasonable question, but I suspect we'd already have some idea if this was the case. There's a lot of artificial light with relatively few, narrow frequencies already in use. I imagine someone, somewhere in some bizarre application would have discovered this as a problem. Since we only see in three color dimensions, it's hard for us to notice day-to-day, but for instance, some fluorescent bulbs are just 5 spikes in particular frequencies. It looks fairly "white" to us, but it's far from normal light. (I am interpreting your comment as being fatigued of/damaged by very specific frequencies in a way that it would not be fatigued/damaged for the same amount of energy spread out over a wider range still within the given cone's sensitivity range.)
- pavel_lishin 7y ago
  > (I am interpreting your comment as being fatigued of/damaged by very specific frequencies in a way that it would not be fatigued/damaged for the same amount of energy spread out over a wider range still within the given cone's sensitivity range.) Yep, that's my concern. I don't know if anyone's done long-term studies about low-level light of identical wavelength. I mean, on the one hand, people used to be afraid of fast-moving vehicles, convinced that it was impossible for a human body to survive going faster than 40 miles per hour. But on the other hand, people used to strap radium to their faces because they thought it was a cure-all, too.

SkyBelow 7y ago

>Photons do not get a special "laser" tag added to them by physics. I thought they kinda did. By being very similar wavelength and power, compared to normal light which has all sorts of wave lengths and power. This difference can mean certain rods/cones being stressed more than average and not triggering the sort of fatigue that normal light would cause. Perhaps the best example of a similar concept, though not with lasers, is looking at a total solar eclipse right before or after the sun is fully eclipsed. There is a small period of time where extremely bright light makes it into our eyes, but not he frequencies that cause pain normally associated with looking at the sun. This means that our default defenses against looking at the sun don't kick in and doing permanent eye damage is extremely easy without feeling any pain as the damage is done.