The exposure limits for lasers in the 1500nm range are almost certainly set by the intensity at which they cause photochemical cataracts. The geometry just doesn't work out for the exposure limits to be set by anything else; a non-visible laser 1500x as powerful as a legal-limit visible-light laser would still only heat the cornea up a hundredth as much as the legal-limit visible-light laser would the retina (intensity at cornea 1/200000th that of intensity at retina, see my comment below [4]). Physical damage to the retina starts around 10 degrees C, so this means that an exposure-limit non-visible laser might change the temperature of your cornea by a tenth of a degree. The normal range for corneal temperature is thirty celsius wide [1, 2] because it's strongly affected by air temperature and air movement. Corneal temperature is controlled to stay below 33-35 Celsius in extremely hot environments (45 C). Studies on microwave burns support this, saying that you have to get rabbit corneas up to 41 degrees C for cataracts to even start to form, implying a reasonable safety factor [3]. Under normal conditions (still air at room temperature), corneal temperature hovers closer to 30 degrees C. A tenth or a hundredth of a degree just isn't going to do anything when the system normally has ten degrees of safety. The vitreous humor varies less but still varies pretty significantly. Conclusion, the exposure limits for 1500nm lasers are not set by thermal damage.
It's generally safe to assume that you're not going to think about this for ten seconds and discover a danger that has been missed by every single person to ever contribute to the exposure limits by thought or by case study.
> It's generally safe to assume that you're not going to think about this for ten seconds and discover a danger that has been missed by every single person to ever contribute to the exposure limits by thought or by case study.
> It's generally safe to assume that you're not going to think about this for ten seconds and discover a danger that has been missed by every single person to ever contribute to the exposure limits by thought or by case study.
Not safe to assume the risks don't exist just because they aren't mentioned in an Ars Technica article.
I would have thought it would be safe to assume a company wouldn't mount a laser on a car that would permanently ruin peoples cameras, but here we are.
I don't believe that the risks don't exist. I believe that what risks exist are extremely unlikely to be something that can be pointed out with a one-line comment on HN. I don't believe that because of this article. I believe that because lasers are unbelievably useful and widely-deployed in industry and tend to cause immediate, visible, and unmistakable damage, so organizations like OSHA have studied them extensively and failures are expensive enough that operators put actual effort into minimizing risk.
> I would have thought it would be safe to assume a
> company wouldn't mount a laser on a car that would
> permanently ruin peoples cameras, but here we are.
I would have thought that that it would be safe to assume that people wouldn't strap 200kW motors to two-ton lumps of metal and send them hurtling around under purely manual control with no physical limits or safety barriers separating them from foot traffic, but here we are.
If the price we pay for eliminating the leading cause of violent death worldwide is that we have to stop pointing cameras at everything, so be it.
It's generally safe to assume that you're not going to think about this for ten seconds and discover a danger that has been missed by every single person to ever contribute to the exposure limits by thought or by case study.
1: https://iovs.arvojournals.org/article.aspx?articleid=2127035 2: http://iovs.arvojournals.org/data/journals/iovs/933602/596.p... 3: https://en.wikipedia.org/wiki/Microwave_burn#Eyes 4: https://news.ycombinator.com/item?id=18887393