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Comment by tennysont | Hacker News Reader

Why wouldn’t your eye lens focus LIDAR photons from the same source onto a small region of your retina in the same way that a phone camera lens focuses same-origin photos to a few pixels?

Sorry if this is a silly question, I honestly don’t have the greatest understanding of EM.

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It's incredibly important to understand that eyes and glass have different optical properties at these wavelengths. It's hard to conceptualize because to us clear is clear, but that's only at visible light. The same way that x-rays and infrared and other spectra can show things human eyes can't see, or can't see things visible light can see, it's a 2 dimensional problem. The medium and the wavelength are both at play. So, when you have the eye which is known to absorb such light, and artificial optics which are known to pass it without much obstruction, they're going to behave like opposites. Imagine if the glass/plastic they used in the car blocked the light. Wouldn't really work.

There is a flip side to this though. Quick searches show that the safety of being absorbed and then dissipated by the water in the eye also makes that wavelength perform worse in rain and fog. I think a scarier concept is a laser that can penetrate through water (remember humans are mostly bags of salt water) which could, maybe, potentially, cause bad effects.

Depends on the wavelength of lidar. Near IR lidars (850 nm to 940 nm, like Ouster, Waymo, Hesai) will be focused to your retina whereas 1550 nm lidars (like Luminar, Seyond) will not be focused and have trouble penetrating water, but they are a lot more powerful so they instead heat up your cornea. To quote my other comment [1]:

> If you have many lidars around, the beams from each 905 nm lidar will be focused to a different spot on your retina, and you are no worse off than if there was a single lidar. But if there are many 1550 nm lidars around, their beams will have a cumulative effect at heating up your cornea, potentially exceeding the safety threshold.

[1] https://news.ycombinator.com/item?id=46127479

Do you if there has been any work how lasers affect other animals and insects?

Am I being catastrophically pessimistic to think that in addition to swatting insects as it moves forward, the cars lidar is blinding insects in a several hundred meter path ?

I’m very optimistic about automated cars being better than most humans but wonder about side effects.

If we have automated anti-mosquito vehicles just roaming around, the world would be a better place. There might be some second order effects from removing mosquitoes that we haven't predicted, but fuck mosquitoes.

Unfortunately not all insects are mosquitoes, and one reason we have many fewer birds in (e.g.) the UK than when I was young, is the decline of insect life.

Follow up question that you might know: would multiple LIDAR sensor actually be additive like that? If you can stand a foot away from a car's LIDAR sensor and be unharmed, then can't you have:

  | Distance | # of Sensors |
  | 1        |            1 |
  | 3        |            9 |
  | 5        |           25 |
  | 10       |          100 |
  | 25       |          625 |
  | 50       |         2500 |
  | 100      |        10000 |

x^2 sensors at x feet from you and have the same total energy delivered? If sensors are actually safe to look at from 6in or 3in, then multiple the above table by 4 or 16.

It seems like, due to the inverse square law, the main issue is how close you can get your eye to a LIDAR sensor under normal operation, not how many sensors are scattered across the environment. The one exception I can think of is a car that puts multiple LIDAR arrays next to each other (within a foot or two). But maybe I'm misunderstanding something!

GP is slightly wrong. IIRC those problematic LIDARs are operating at higher power than traditionally allowed, with the justification that the wavelength being used is significantly less efficient at damaging human eyes, therefore it's safe enough at those powers, which is likely true enough. But it turned out that camera lenses are generally more transparent than our eyes and therefore the justification don't apply to them.

Amusingly the lenses are worse than silicon at transmitting that wavelength.

1550nm might be worse for sensors because a good portion of the light is only being dumped into the metal layers - pure silicon is mostly transparent to 1550nm. Not sure how doped silicon would work. I can tell you that 1070nm barely works on an IQ3 Achromatic back…

https://www.pmoptics.com/silicon.html

Your eyes a much larger sensor area than the opening, they do the opposite of concentrating light in a small area.

A point source in the visual field will create a point image on the retina. The "sensor area" you're referring is what's necessary to capture the entire visual field simultaneously.

I disagree that it’s a point source at distances of peak concern.

Also, it’s something of a nitpick but physically point sources still end up as a circle.

That's fair, strictly speaking, but I'm not sure there's a meaningful difference to be made.

Wasn't sure what level of knowledge you were coming from re: PSFs, so I was keeping it basic.

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