[HN Gopher] All about automotive lidar
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All about automotive lidar
Author : dllu
Score : 59 points
Date : 2025-12-01 17:43 UTC (1 days ago)
(HTM) web link (mainstreetautonomy.com)
(TXT) w3m dump (mainstreetautonomy.com)
| CGMthrowaway wrote:
| Adding a comment here with some info on LIDAR human safety, since
| many are asking.
|
| There are two wavelengths of interest used: a)
| 905 nm/940 nm (roof and bumpers): 70-100 uJ per pulse max,
| regulated by IEC 60825 since this WL is focused on the retina
| b) 1550 nm systems (the Laser Bear Honeycomb): 8-12 mJ per pulse
| allowed (100x more photons since this WL stays the cornea)
|
| The failure mode of these LIDARs can be akin to a weapon. A stuck
| mirror or frozen phased array turns into a continuous-wave pencil
| beam. A 1550 nm LIDAR leaking 1W continuous will raise corneal
| temperature >5C in 100ms. The threshold for cataract creation is
| only 4C rise in temp. A 905 nm Class 1 system stuck in one pixel
| gives 10 mW continuous on retina, capable of creating a lesion in
| 250ms or less.
|
| 20 cars at an intersection = 20 overlapping scanners, meaning
| even if each meets single-device Class 1, linear addition could
| offer your retina a 20x dose enough to push into Class 3B
| territory. The current regs (IEC 60825-1:2014) assume single-
| source exposure. There is no standard for multi-source, multi-
| axis, moving-platform overlay.
|
| Additionally, no LIDAR manufacturer publishes beam-failure
| shutoff latency. Most are >50ms, which can be long enough for
| permanent injury
| addaon wrote:
| > There are two wavelengths of interest used
|
| Ouster uses (or at least used to use, not sure if they still
| do) 840 nm. Much higher quantum efficiency for standard silicon
| receivers, without having to play games with stressed silicon
| and stuff; but also much better focusing by the retina, so
| lower power permitted.
| krackers wrote:
| I was always curious about this, it's impossible to find any
| safety certifications or details about the lidars used by e.g.
| Waymo. Are we supposed to just trust that they didn't cut
| corners, especially given the financial incentives to convince
| people that lidar is necessary (because there's a notable
| competitor that doesn't use it).
|
| To date most class-1 lasers have also been hidden/enclosed I
| think (and there is class 1M for limited medical use), so I'm
| not convinced that the limits for long-term daily exposure have
| been properly studied.
|
| Until I see 3rd party studies otherwise, I plan to treat
| vehicle lidar no different than laser pointers and avoid
| looking directly at them. If/when cars become common enough
| that this is too hard to do, maybe I'll purchase NIR blocking
| glasses (though most ones I found have an ugly green tint, I
| wonder if it's possible to make the frequency cutoff sharp
| enough that it doesn't filter out visible reds).
| Zigurd wrote:
| Every day dozens of Waymos are in close proximity to the
| people cleaning them and plugging them in, and they are
| maneuvering in tight spaces amongst other Waymos. That's not
| a peer reviewed study, but it seems to work.
| addaon wrote:
| A quick note about units -- you correctly quote the limits as
| an energy-per-pulse limit. The theory behind this is that
| pulses are short enough that rotation during a pulse is
| negligible, so they tend to hit a single point (on the retina,
| at focusable frequencies; the cornea itself for longer wave
| lengths), and the absorption of that energy is what causes
| damage. But LiDAR range is determined not by energy per pulse,
| but by power. This drives a desire for minimum-time pulses,
| often < 10 ns -- if you can halve your pulse length, you can
| increase your range substantially while still being eye-safe.
| GaNFETs are one of the enabling technologies for pulsed lidar,
| since they're really the only way out there to steer tens of
| amps in single-digit nanoseconds. Even once you've solved
| generating short pulses, though, you still need to interpret
| short responses. Which drives either a need for very fast ADCs
| (gigasample+), or TDCs, which are themselves fascinating
| components.
| dllu wrote:
| The article talks about eye safety a bit in section 4.
|
| > a stuck mirror
|
| This is one of the advantages of using an array of low power
| lasers rather than steering a single high power laser. The
| array physically doesn't have a failure mode where the power
| gets concentrated in a single direction. Anyway, theoretically,
| you would hope that class 1 eye-safe lidars should be eye safe
| even at point blank range, meaning that even if the beam gets
| stuck pointing into your eye, it would still be more or less
| safe.
|
| > 20 cars at an intersection = 20 overlapping scanners, meaning
| even if each meets single-device Class 1, linear addition could
| offer your retina a 20x dose enough to push into Class 3B
| territory.
|
| In the article, I point out a small nuance: 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.
|
| Also, if a lidar is eye-safe at point blank range, when you
| have multiple cars tens of meters away, laser beam divergence
| already starts to reduce the intensity, not to mention that
| when the lidars are scanning properly, the probability of all
| of them pointing in the same spot is almost impossible.
|
| By the way, the Waymo Laser Bear Honeycomb is the bumper lidar
| (940 nm iirc) and not the big 1550 nm unit that was on the
| Chrysler Pacificas. The newer Jaguar I-Pace cars don't have the
| 1550 nm lidar at all but have a much bigger and higher
| performance spinning lidar.
| ErroneousBosh wrote:
| > > a stuck mirror
|
| Detect the mirror being stuck and shut the beam off. Easy.
|
| Hint: how bad would it be if the MCU in your gas heating
| boiler latched up and wouldn't shut the burner off? How is
| this mitigated?
| observationist wrote:
| Enormous complexity, safety risks, and completely unnecessary
| for successful level 4 FSD - the hurdle to full autonomous
| driving was basically jumped by Tesla this year. I don't see
| why lidar is even allowed in public at this point, it seems
| dangerous enough that you'd want it effectively restricted to
| highly regulated and licensed uses, like military or academic
| scanning, with all sorts of deliberate safeguards and liability
| checks.
|
| Social media is full of little clips of lidar systems burning
| out camera pixels, and I'm sure big proponents of the tech have
| paid people off over eye injuries at this point. There've
| probably been a ton of injuries that just got written off as
| random environmental hazards, "must have looked at the sun"
| etc.
|
| It's nuts that this stuff gets deployed.
| AlotOfReading wrote:
| the hurdle to full autonomous driving was basically jumped by
| Tesla this year.
|
| Tesla doesn't have driverless operations anywhere, and their
| Austin fleet consists of <30 vehicles with full time safety
| drivers that have a far worse safety record than Waymo
| vehicles.
|
| It's not nothing, but it's a _long_ way from being a complete
| system (let alone the obviously superior one).
| addaon wrote:
| Having built a LiDAR system for an autonomy company in the past,
| this is a great write-up, but it omits what I found to be one of
| the more interesting challenges. For our system (bistatic,
| discrete edge-emitting laser diodes and APDs; much like a
| Velodyne system at high level), we had about an inch of
| separation between our laser diodes and our photodiodes. With 70
| A peak currents through the laser diodes. And nanoamp sensitivity
| in the photodiodes. EMI is... interesting. Many similar lidars
| ignore the problem by blanking out responses very close to firing
| time, giving a minimum range sensitivity, and by waiting for
| maximum delay to elapse before firing the next salvo -- but this
| gives a maximum fire rate that can be an issue. For example, a 32
| channel system running at 20 kHz/channel would be limited to ~200
| m range (468 m round trip delay, some blanking time needed)... so
| to get both high rate (horizontal resolution) and high channel
| count (vertical resolution), you need to be able to ignore your
| own cross-talk and be able to fire when beams are in flight.
| newpavlov wrote:
| >we had about an inch of separation between our laser diodes
| and our photodiodes
|
| Why can't you place them further away from each other using an
| additional optical system (i.e. a mirror) and adjusting for the
| additional distance in software?
| addaon wrote:
| You can, but customers like compact self-contained units. All
| trade offs.
|
| Edit: There's basically three approaches to this problem that
| I'm aware of. Number one is to push the cross-talk below the
| noise floor -- your suggestion helps with this. Number two is
| to do noise cancellation by measuring your cross-talk and
| deleting it from the signal. Number three is to make the
| cross-talk signal distinct from a real reflection (e.g. by
| modulating the pulses so that there's low correlation between
| an in-flight pulse and a being-fired pulse). In practice, all
| three work nicely together; getting the cross-talk noise
| below saturation allows cancellation to leave the signal in
| place, and reduced correlation means that the imperfections
| of the cancellation still get cleaned up later in the
| pipeline.
| jandrese wrote:
| 200m range seems adequate for passenger vehicle use. Even at
| 100kph that's over 7 seconds to cover the distance even if you
| aren't trying to slow down. I think there is diminishing
| returns with chasing even longer ranges. Even fully loaded
| trucks are expected to stop in about 160m or so.
| addaon wrote:
| Yep, 200 m is pretty close to standard. Which is why 32
| channel and 20 kHz is a pretty common design point. But
| customers would love 64 channel and 40 kHz, for example.
| Also, it's worth noting that if your design range is 200 m --
| your beam doesn't just magically stop beyond that. While the
| inverse square law is on your side in preventing a 250 m
| target from interfering with the next pulse, a retro-
| reflector at 250 m can absolutely provide a signal that
| aliases with a ~16 m signal (assuming 234 m time between
| pulses) on the next channel under the right conditions. This
| is an edge case -- but it's one that's observable under
| steady-state conditions, it's not just a single pulse that
| gets misinterpreted.
| Animats wrote:
| No mention of flash LIDAR, which really ought to be seen more for
| the short-range units for side and rear views.
|
| Interference between LIDARs can be a problem, mostly with the
| continuous-wave emitters. Pulsed emitters are unlikely to collide
| in time, especially if you put some random jitter in the pulse
| timing to prevent it. The radar people figured this out decades
| ago.
| dllu wrote:
| A flash lidar is simply a 2D array of detectors plus a light
| source that's not imaged. It's mentioned super briefly at the
| start of section 3 but you're right, I should have gone into
| more detail given how common and important they are.
|
| For pulsed emitters, indeed adding random jitter in the timing
| would avoid the problem of multiple lidars being synced up and
| firing at the same time. For some SPAD sensors, it's common to
| emit a train of multiple pulses to make a single measurement.
| Adding random jitter between them is a known and useful trick
| to mitigate interference. But in fact it isn't super accurate
| to say that interference is a problem for continuous-wave
| emitters either. Coherent FMCW lidar are typically quite robust
| against interference by, say, using randomized chirp patterns.
| rappatic wrote:
| In the current state of self-driving tech, lidar is clearly the
| most effective and safest option. Yet companies like Tesla refuse
| to integrate lidar, preferring to rely solely on cameras. This is
| partially to keep costs down. But this means the Tesla self-
| driving isn't quite as good as Waymo, which sits pretty
| comfortably at level 4 autonomy.
|
| But humans have no lidar technology. We rely almost solely on
| sight for driving (and a tiny bit on sound I guess). Hence in
| principle it should be possible for cars to do so too. My
| question is this: at what point, if at all, will self-driving get
| good enough to make automotive lidar redundant? Or will it always
| be able to make the self-driving 1% better than just cameras?
| convenwis wrote:
| There are unquestionably some cases where Lidar adds actual
| data that cameras can't see and is relevant to driving
| accuracy. So the real question is whether there are cases where
| Lidar actually hurts. I think that is possible but unlikely to
| be the case.
| readthenotes1 wrote:
| Many humans do a really bad job at driving, so I'm not sure we
| should try to emulate that.
|
| And it is certain that in India they use sound sound for
| echolocation.
| rappatic wrote:
| > Many humans do a really bad job at driving, so I'm not sure
| we should try to emulate that
|
| Agreed, but there are still really good human drivers, who
| still operate on sight alone. It's more about the upper
| bound, not the human average, that can be achieved with only
| sight.
| Zigurd wrote:
| That upper bound can be pretty low in bad lighting
| conditions. If you have no strategy to work around that,
| your performance is going to be bad compared to vehicles
| with radar and lidar. On top of all that, Waymo's
| performance advantage might come in part from the
| staggering amount of geospatial data available to Waymo
| vehicles and unique to Waymo's parent company.
|
| The second and third place companies in terms of the number
| of deployed robotaxis are both subsidiaries of large
| Chinese Internet platforms, and both of them are also
| leaders in providing geospatial data and navigation in
| China. Neither operates camera-only vehicles.
| floatrock wrote:
| > My question is this: at what point, if at all, will self-
| driving get good enough to make automotive lidar redundant?
|
| By 2018, if you listen to certain circa-2015 full self-driving
| technologists.
| thechao wrote:
| Let's just do a quick comparison: the visual cortex consumes
| about 10x more volume of the human brain than the language
| center. So... that's a rough comparison of difficulty. I seem
| to remember the visual centers is also a lot older,
| evolutionarily than the language centers?
| Barathkanna wrote:
| I learned a lot from this article. The breakdown of the different
| LiDAR types and how they fit into real automotive sensor stacks
| was especially helpful. Nice to see a clear explanation without
| the usual hype or ideology around cameras vs. LiDAR.
| ge96 wrote:
| The discrete array, must be accurate for them to be close like
| that and not get overlap (eg. receiver 1 gets beam from emitter
| 2)
| xattt wrote:
| I am surprised that I didn't see discussion about Audi's lidar
| that's been in use in production vehicles now. Yes, it's on a
| different level, only used for ADAS, but it's still lidar that's
| actively used.
| dllu wrote:
| If I remember correctly, the Valeo Scala that's in the Audi
| cars uses a discrete 16 element 1D array (940 nm diodes + APDs)
| plus a rotating mirror to scan.
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