Hacker News Reader

Comment by 6stringmerc | Hacker News Reader

It will be interesting, to me, if there are any observable effects on nature exposed to 200 meter blasts of IR type wavelength stuff.

I mean, maybe it'll scare off deer, or pull them in closer to see what's up? Any number of species with un-intended consequences. Insects in the desert. Pidgeons in the big city. Gulls on the coast.

Maybe it's totally harmless, but I'd like a study that verifies mass adoption would not have ecological consequences.

View on HN

Your comment spurred me to search for information about near-infrared vision systems in animals. NIR vision appears to be entirely absent from vertebrates. (I am not claiming that it is present in invertebrates, only that I found stronger claims about absence from vertebrates.)

See "The Verriest Lecture 2009: Recent progress in understanding mammalian color vision"

https://pdfs.semanticscholar.org/c9df/0b61e4a45e10577c001513...

Particularly Figure 1. Vertebrate photopigment sensitivity drops off rapidly toward the near IR (~700 nm).

I found this fascinating related (but not peer reviewed) document on arXiv, "Did Evolution get it right? An evaluation of near-infrared imaging in semantic scene segmentation"

https://arxiv.org/pdf/1611.08815.pdf

The author performs semantic segmentation with convnets using conventional visual-spectrum images and compares performance with images spectrally extended into the near-infrared. He finds that adding the additional NIR band did not improve task performance -- hence that evolution "got it right" by not expanding vision into a wavelength region that fails to improve semantic segmentation. I'm not sure how good this work is from a professional biologist's perspective, but I found it damn interesting.

EDIT: note that this laser operating at 1550 nm is far from the long wave IR (~8000 nm and up) that various animals sense to detect prey body heat.

I believe that I can't see that wavelength, but the energy has to go somewhere (similarly, I can't see microwave radiation, but don't want to put my head in a running microwave, a la Infinite Jest). I think the better question is: Will it blind you/me/animals?

Indeed, I find it mildly painful to look at IR emitters, for example, on a "night vision" security camera. I don't believe it is dangerous or will blind anyone, or anything, but it is plausible to me that there could be an unanticipated effect.

EDIT: It appears that this is given a passing mention in the article:

. . . it can receive at a wavelength of 1550 nanometers, deep in the infrared part of the spectrum. That makes this wavelength much safer for human eyes than today’s standard wavelength, 905 nm.

It depends on the power density. I have an IR laser that is invisible and it would burn your eyes out of your head.

~40 mW peak, ~10 nS pulses

>similarly, I can't see microwave radiation, but don't want to put my head in a running microwave, a la Infinite Jest

Yet wireless access points spew microwave radiation at you all day.

Not at 1,000W.

However, you do receive a couple hundred watts of near infrared radiation (ie the 1550 nm in the laser) just by being in direct sunlight:

https://en.wikipedia.org/wiki/Sunlight#/media/File:Solar_spe...

But even though I can't see it, I can definitely feel it.

The premise of the parent comment is that even invisible lasers could be harmful. You pointed out that microwaves may not be as harmful at lower levels of power. I pointed out that the output of a lidar beam is far below the level that you get from sunlight, which doesn't even cause cancer and certainly doesn't blind people.

Just because I like running numbers, here's the comparison: the laser in this lidar has a power of ~40 mW, ~1000x less than sunlight. Lidar pulses are on the order of 10 nanoseconds, 100,000,000x less than a second. The energy on your eyes is less than 100 billion times less than a second in bright sunlight. There is certainly no mechanism for thermal damage to occur.

40mW would be dangerous for a constant laser (class 3b), but I'm not sure about a short pulsed one. I think you should look at the amount of energy per pulse.

It would be class 3r, for which direct retina exposure is "low risk". In general for pulsed lasers you can use the duty cycle. I did more analysis in another comment:

Using a maximum permissible exposure chart gives a better sense of danger. Lidar pulses are on the order of 10 nanoseconds, or 1/100th the smallest division on this chart[2]. Even so, you can see that the maximum safe power for 1550 nm is somewhere between 8 and 10,000 watts, at least 800x more than the lidar emits.

1550 nm doesn't chemically damage biological receptors. The damage would have to be thermal, but the laser is pulsed for an incredibly short time and even if it wasn't it's well under what you can be exposed to indefinitely.

[2] https://en.wikipedia.org/wiki/File:IEC60825_MPE_W_s.png

> the output of a lidar beam is far below the level that you get from sunlight, which doesn't even cause cancer and certainly doesn't blind people

Sunlight certainly does cause cancer, although we generally attribute that to the UV in sunlight. Sunlight is also well-known for blinding people.

The near-1550 nm wavelengths do not cause cancer or blind people.

Just to add to your comment, even so that the energy in each pulse is less than 100 billion times less than the energy from bright sunlight emitted in a second, it is still significant, but the number of laser pulses per second is key to knowing if the (peak) intensity of the laser is dangerous to humans or not, as they accumulate over said second. If you only had one pulse per second at 40 mW you would be looking at 30 mJ of energy per pulse, capable of making a nice plasma in air if focused, or machining metal. However they are probably working at 100s of kHz in order to be able to measure an image fast enough, so the energy per pulse is much lower. Key here is the fact that our eye's lens doesnt transmit 1550nm so well, so the interaction with the eye doesnt involve focused light on the retina, hence the interaction intensity is much lower as the light is spread over most of the surface of the eye. Hence they can use much more power and still be eye safe/class 1 or 2, because whatever light gets to the eyes never gets focused down to a tiny spot in the retina, unlike visible lasers.

Also, sunlight is specified in intensity (power/area), and here we only have laser power, not laser spot size, so it is hard to make a fair comparison. nevertheless, sunlight is roughly ~1kW/m^2, so if the laser had a spot size of 2 mm (required to be this big for diffraction over hundreds of meters of propagation to not reduce its intensity too much) we can calculate the power of sunlight in that area: 3 mW. So the laser would be actually ~10x more intense. (if the laser would be 7.2 mm wide then the intensity would be the same as sunlight) But one is comparing totally different wavelengths, so the laser safety rules are different. Two intros to laser safety for whomever is interested: https://www.rp-photonics.com/laser_safety.html https://spie.org/Documents/Publications/00%20STEP%20Module%2...

About thermal damage - funnily enough there is lots of time in nanoseconds to transmit heat and cause thermal damage. Heat transfer is actually reasonably fast at the submicroscale. As a curiosity see https://www.semrock.com/Data/Sites/1/semrockimages/technote_... for the difference between punching a hole with a femtosecond laser (no time for thermal diffusion to happen) and a nanosecond pulsed laser. The area around the laser just completely melts in the nanosecond case. Nevertheless this was done at much higher energies per pulse than the lidar lasers (thankfully!)

>If you only had one pulse per second at 40 mW you would be looking at 30 mJ of energy per pulse

40 mW peak power, not average power. Average power somewhat less, maybe 20 mW.

>Also, sunlight is specified in intensity (power/area), and here we only have laser power, not laser spot size, so it is hard to make a fair comparison.

With sunlight and with a laser scanner, the entire body will be illuminated with that power, very roughly. If you stand directly in front of the laser scanner that 40 mW will fall over your entire body, and a similar fraction of the energy will go into your eyes as with sunlight.

The laser in the article is on the order of tens of milliwatts. Even directly into your eye would not damage it. It would be painful, especially if it was in a visible wavelength, but the laser spot from a lidar is in one location for less than a microsecond.

In terms of direct heating, tens of milliwatts isn't even enough to really make a human-detectable rise.

> is in one location for less than a microsecond

When it is working properly.

And self-diagnostics will know when it isn't.

Same with elevators, microwaves, airbags, and in fact literally anything that plugs into the wall. 120 volts can kill you if you contact it.

The laser is eye-safe, meaning you can look directly at it continuously and be fine. Though, if you did, you would deserve injury. Kind of like sticking your hand in a blender.

The device will not manage to malfunction and miraculously shoot you in the eye from meters away.

Would it even be painful at that wavelength?

No, although lasers can sometimes be dangerous without being painful. Even if they aren't, by the time it hurts it is too late.

Vampire bats use modified capsaicin (chili pepper) receptors in their nose to detect infrared light:

https://www.nature.com/nature/journal/v476/n7358/full/nature...

They use this to find their warm-bodied prey, but of course it's only detection, not vision.

I learned this today, and now I'm happy I did.

Pit vipers too. The pits are used to 'see' infrared.

Thank you. Definitely the coolest thing I will learn today.

I was about to ask if you work where I do, then I saw your username, then I remembered that you hired me through HN..

You guys seem to have amazingly interesting jobs. Please hire me, I'm your future-colleague.

sci-hub link https://sci-hub.ac/https://www.nature.com/nature/journal/v47...

Pit Vipers can sense IR with a secondary sight organ called a fossa. https://en.wikipedia.org/wiki/Pit_viper

>> He finds that adding the additional NIR band did not improve task performance

But did they try in low light? It seems that seeing in IR should help with detection of predators or prey at night.

IR near the visible range is associated with night vision because we use active night vision goggles that use an infrared spotlight at 850 or 940 nm wavelengths (700 nm is red). This is not particularly useful without an illuminator, you're basically just getting visible light amplification then.

Passive thermal vision that might pick out a warm object in the dark require sensing of ~10,000 nm/10 um infrared, a very different problem! And one that wouldn't be easy to solve biologically, as it basically requires being colder than the object you are sensing. Edit: but not impossible! https://en.m.wikipedia.org/wiki/Infrared_sensing_in_snakes

Are you referring to sensing body heat of other animals? That's a long wave IR emission, ~8000 nm and up. Some animals do indeed sense that and it is quite useful at night. This laser, and the paper I linked to, are operating with much shorter IR wavelengths (~800 to 1550 nm). This spectral region overwhelmingly comes from sunlight under natural conditions, and its intensity drops sharply at night like the ordinary visible range.

Nocturnal animals function by having a large proportion of rods. This was true of our anthropoid ancestors, resulting in humans having very limited high acuity color vision. We get round this by rapidly scanning and stitching the world together (the inability to do this is a sore problem for visual prosthesis). That the world seems sharp and rich in color is a testament to the feats of predictive inference our brains regularly perform.

One thing is that water has absorption bands at 970nm, 1200nm, 1450nm, and 1950nm, and eyes have a lot of water in them. So they simply aren't very transparent in the near infrared.

Also, why would you evolve eyes tuned to wavelengths that don't penetrate water well? That seems maladaptive in an aquatic environment.

https://en.m.wikipedia.org/wiki/Electromagnetic_absorption_b...

Why would you evolve eyes that could see wavelengths that don't penetrate your environment?

Yeah, why would you?

I'm not sure if this exchange means that there is no good reason to do that, or if it means that the reason why one would want to do that is blindingly obvious to everyone except me. :)

The reason you want to see wavelengths that don't penetrate your environment is so that you can see your environment.

None of that light would ever reach your eyes for you to see it, though, right? Or am I missing something really obvious?

Maybe I should have elaborated a bit more. My original point was that it makes sense that the visible spectrum was colocated with the frequencies not readily absorbed by water.

Which is to say, eyes were made for seeing the light that was bouncing around in the sea (and not the frequencies that had already been absorbed).

So yes, the simplest answer you can imagine.

Right, that makes perfect sense. I'm mostly unsure of what tempestn said.

Also to the same point: eyes evolved to see the wavelengths where the Sun outputs the majority of its energy, which is a significant factor in its ability to penetrate water to any depth.

Yeah, if the water is the surroundings.

I was answering the broader question of not wanting light to penetrate "your surroundings" - ie the desk in front of me or walls around me. Would make life difficult if everything was transparent. Normally when one talks about "surroundings" it means that stuff, not the air (analogous to the water for marine life) both of which obviously need to be at least somewhat transparent for vision to be useful.

In that case, how well will this new lidar work in the rain?

Rain is actually very little water at any one path. A drop is falling at 10 meters per second and heavy rain is ~1 cm per hour. So to ballpark it's around 1 part in 3.5 million water on average and assuming 1mm drop size you will see ~3.6km on average before you encounter a drop.

Note this is instantaneous, human vision deals with after images which adds blur.

That's a good calculation. http://hypertextbook.com/facts/2007/EvanKaplan.shtml backs up your facts and claims that a raindrop is actually more like 6 mm, which makes the straight line view much longer.

However in the rain, on a highway, we have water falling, water splashed up from the ground, a mist formed by cars, high humidity, and a wet layer on the outside of the car. These factors reasonably could impact this device if the laser is emitting at water's absorption frequency.

I currently work on a self-driving lorry, we get around this issue by installing over a dozen lidars.

It's worth pointing out that there are aircraft mounted LiDAR systems that already operate at 1550nm, such as [0]. Another company has an interesting paper about which wavelength is best for their activities[1].

http://www.teledyneoptech.com/index.php/product/titan/

[1] (PDF!) http://www.riegl.com/uploads/tx_pxpriegldownloads/Paper_ILMF...

Considering ~55% of the sun's energy that hits the earth is in the form of IR, my guess is IR systems would be marginal. I think it bears testing though to be sure.

As you say other creatures are much more sensitive to IR differences.

That's a good point, but also reminds me of moths circling a flame or porch light. The vast majority of light we see in the world comes from the sun, but when the sun is elsewhere, our artificial light triggers changes in how insects behave.

I wonder if ground-source lidar at night would have similar effects on animals that are "used to" IR coming from above.

This wavelength of light is used for long range telecomms. We would know if it did anything. Animals can't see this wavelength, not even snakes or fish. In addition to that the laser spot is spread rapidly over a very wide area and it won't actually be visible except to extremely fast sensors, which eyes are not.

1500nm is way outside the the range of usable solar radiation in nature.

https://upload.wikimedia.org/wikipedia/commons/e/e7/Solar_sp...

Snakes pick back up around 5000nm since that's the temperature other living animals radiate, which is helpful in hunting. https://en.wikipedia.org/wiki/Infrared_sensing_in_snakes

This is a good point. But same goes for other sensors in cars. I always wondered how annoying AF ultra-sonic sensors are for dogs. It looks like most ultrasonic sensors are out of range for dogs, but the ultrasonics for sure mess with bats. I wonder how bat populations will be affected when all of these ultrasonic sensors mess with their ability to hunt.

Cops in my city installed subsonic sirens on their cars to alert people who are playing loud music etc. Its always bothered me a bit about not knowing the potential impact to animals

Ultrasound transducers are not the only producers of ultrasound, nor the loudest. Most things that vibrate create ultrasound, including almost anything that moves. Noise pollution is mostly produced accidentally.

Also, nocturnal bats will largely be unaffected by cars in no small part because they don't cohabitate with humans very much.

Can I direct your attention to the street lights? Those death traps, causing millions of insects to fly in circles and possibly die of exhaustion.

You will save many more insects, raising awareness to this problem.

Exactly we are blasting so much radiation everywhere, why should we start caring now with the IR radiation.

The best way to start fixing a problem is to stop making things worse.

LIDAR may or may not have an adverse impact on wildlife, but we should at least find out and see if there are simple ways to mitigate any possible side effects.

Deer cannot see at 1550 nm. I'm not aware of any mammals that can.

What you care about is the maximum permissible exposure at close range - because it's entirely possible that a kid is going to walk up to your car and stick their face up against the glass. The laser beam will already be fairly wide (order of mm) as it exists the system, but it needs to be reasonably low divergence to give you accurate spatial information 200 m away. We should assume to be pessimistic, that you get the full beam into your eye (up to 7 mm).

This is really back of the envelope stuff, but there are lots of factors to consider. You could probably get away with even a 100mW laser with the right setup. Obvious disclaimer that you should respect laser safety and not trust someone's internet napkin calculations.

According to this you're allowed 1W/m^2 at > 1400nm for an accidental exposure (100 seconds): https://workspace.imperial.ac.uk/physics/Public/physicsdocs/...

Equivalently that's 1 mW/mm^2. So the question is, what power is the laser kicking out? A Faro scanner can put out as much as 20mW/mm^2 at 1m and their systems are thus Class 3R. So far, so bad.

However... laser safety ratings are given as "Under normal operating conditions". The laser is being scanned, and very quickly at that, so you'd only be getting very short bursts of light (I don't know if it's truly a pulsed laser). If you stared into the beam continuously you would have problems, but since the beam is only going to hit you for a fraction of a second it's unlikely to do any damage. And indeed Faro say that for practical purposes their system is eye-safe, even though it's got a stonking laser in it.

The tables say you can go up to 10^4 J/m^2 for short exposures and suppose we only have the beam in our eye for 10^-3 seconds (additionally the pulse length will be very short), you're allowed a light power of perhaps 1000 times higher. Maybe divide by a factor of 100 or so because you'd get several repeat exposures if you stood in the same place or if you're standing on a street filled with these things.

Have a look at Faro's manual, Appendix E for a real example of this kind of analysis: https://doarch332.files.wordpress.com/2013/11/e866_faro_lase...

I don't know about IR but Kestrel's (the bird) are UV sensitive. AFAIK all organics emit IR so it's probably not going to be a problem.

Many types of common headlights, and other light sources, emit tons of IR radiation already so we'd probably know.

Fish are sensitive to IR, it penetrates water better than visible or UV.

> IR, it penetrates water better than visible or UV.

What? IR is lower energy than visible red and that's the first color to go when you get a few feet under water (with no local light source).

Water does absorb infrared well but it's not because it has lower energy. Infrared is absorbed well due to the spectrum of vibrational transitions. Ultraviolet is also absorbed well, due to electronic transitions. There is a "window" in the visible light that is not absorbed well by many transitions.

> but it's not because it has lower energy...There is a "window" in the visible light

fair enough, I got my physics a bit wrong there, but I was under the impression that that window was in the blue/green part of the spectrum since I do know that water is good at blocking UV and even cosmic radiation.

I also know that it's good at blocking visible red, because if you go further than about 20-30 feet down on a sunny day and cut yourself, your blood looks green.

Is there an additional window in the infrared part of the spectrum that supports GP's point?

some fish see some IR. Carp etc. would be able to see the 900 nm light in normal lidar, but even they can't see 1550 nm.

Reply on news.ycombinator.com