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Most current self driving car lidars operate close to the 900 nm range, and they are required to output 1000 times less power than the 1550 nm lidar in this article. [1] So far these seem totally harmless to cameras.

1550 nm lidars for self driving cars are a relatively recent thing with only a handful of companies (AEye, Luminar, Blackmore) making them. The benefit is that, thanks to the extra power, they have longer range. Unfortunately they fry cameras and are very expensive.

It's also worth pointing out that the 1550 nm pulsed lidars like AEye and Luminar with fiber lasers may have much shorter pulses than the 5 ns pulses of, say, a 905 nm Velodyne lidar. So, not only is the average power 1000 times higher, but the peak power may be even higher.

[1] https://en.wikipedia.org/wiki/File:IEC60825_MPE_J_nm.png






The relevant part of the article: "But it also has a big advantage: the fluid in the human eye is opaque to 1550nm light, so the light can't reach the retina at the back of the eye. This means lasers can operate at much higher power levels without posing an eye safety risk. AEye uses 1550nm lasers. And unfortunately for Chowdhury, cameras are not filled with fluid like human eyes are. That means that high-power 1550nm lasers can easily cause damage to camera sensors even if they don't pose a threat to human eyes."

I imagine it is doing something to the fluid in the eye with that kind of energy it absorbs. Maybe cataracts for example.

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.

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


> 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.

But then what would HN be for?


> 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.


> Not safe to assume the risks don't exist just because they > aren't mentioned in an Ars Technica article.

https://www.lesswrong.com/posts/zsG9yKcriht2doRhM/inadequacy...

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.


Exactly, it's the same with unshielded microwaves, and it's astonishing that someone would think it's safe to crank the power on these lasers with that justification.

> When injury from exposure to microwaves occurs, it usually results from dielectric heating induced in the body. Exposure to microwave radiation can produce cataracts by this mechanism,[28] because the microwave heating denatures proteins in the crystalline lens of the eye (in the same way that heat turns egg whites white and opaque). The lens and cornea of the eye are especially vulnerable because they contain no blood vessels that can carry away heat.

https://en.wikipedia.org/wiki/Microwave#Effects_on_health


But wouldn't that be true of all electromagnetic radiation that's absorbed by the fluid? I can't imagine this being more harmful than looking at a sunset from the pov of total energy being pumped into the eyeball. Or walking outside at mid-day among shiny buildings.

It is quite easy to believe that as-lased from lasers in the lidar units, the beams are generally safe. But could other optical mechanisms such as eye-glasses accidentally focus these dispersed beams in such a way that they could again be dangerous?

But if eye-glasses could do that, then people would get retinal burns from the sun, and so on. Remember that all glasses do is adjust the path of light reaching the lens of the eye so that when it arrives at the retina it is identical to the path of light focussed by a normal, healthy eye. Which also means that another way we know it isn't a problem is that people without glasses are safe.

Also, remember that this is medium-wavelength IR at 1500nm, which is between two and three times the wavelength of visible at 400-700nm approximately. The energy in a photon is calculated as E = hf = hc/l where h is Planck's constant and c is the speed of light, while l is the wavelength. Notice how the energy decreases nice and linearly as the wavelength increases - this is good!

the human eye might not be affected, but are any animals or insects susceptible to these wave lengths ?

plus are there any weather conditions the light become visible?


There are absolutely no weather conditions that can transform this near-IR into visible light.

It's worth noting that the Blackmore system is continuous wave and much lower power than AEye and Luminar, so idk if the same thing would happen to cameras

So why do they use pulsed light? What’s the benefit of time-of-flight over the continuou method? Can signal to noise of time of flight ever approach the correlation methods?



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