> The device can thus see far without having to turn up the brightness. That’s important because the sensor works at 905 nanometers, an eye-sensitive wavelength the company chose because it works with silicon. You need exotic compound semiconductors to make and detect laser light at 1550 nm, a wavelength that’s easier on the eyes
905 nm is infrared, outside the visible range for humans. If someone made a LIDAR at that wavelength, and did "turn up the brightness", what kind of damage would it do to people? Is the danger increased because it is not visible, so you don't have a clue that you are looking at something dangerously bright?
> The retina does not respond to the 905-nm infrared light used in current car lidars, so we can’t see it. But the eye transmits 905 nm to the retina, so it’s subject to the same restrictions as visible light. In fact, it’s even more hazardous because the eye cannot automatically turn away from a bright source that the retina can’t sense.
The eye is opaque to 1550 nm light, and so even if you are looking right at it none of it makes it to the retina.
Which isn't to say that 1550 nm light is safer -- the mode of destruction is just different, e.g. corneal damage leading to cataracts or surface burns rather than retinal damage.
As I understand it, it’s largely a focusing issue. Close to the visible range, a distant point source gets focused to a point on the retina. At 1550nm, the energy is deposited uniformly on the cornea unless the laser is focused to a tiny spot on the cornea.
edit: I don’t know to what extent this is relevant, but humans can regenerate the corneal epithelium. Think about all the sand you’ve gotten in your eye as a kid, and the fact that it probably didn’t accumulate enough damage to blind you.
Typically you select a class of laser safe for the environment it will be used in -- class 1 is typical of LIDAR systems for this reason which poses no eye damage risk.
The lasers in these things are often not class 1, but the whole system is. Perhaps it's fairer to say that laser classification is not just about the power of the laser, it's about how it's used and under what conditions. Class 1 basically means that it's safe under normal operation. You can look at the certifications for scanning stations (e.g. Faro put theirs online) and they usually get round it by specifying that the system is spinning, so you don't get hit with a laser that often, and that you're standing far enough away that the divergence is large.
If you somehow fixed the laser and stared into it, it would probably hurt.
according to the test report, if the mirror fails, you would hit dangerous levels of energy deposited within 0.2s and they recommend that the laser must be turned off within 100ms to avoid risk of eye damage.
905 nm is infrared, outside the visible range for humans. If someone made a LIDAR at that wavelength, and did "turn up the brightness", what kind of damage would it do to people? Is the danger increased because it is not visible, so you don't have a clue that you are looking at something dangerously bright?