> I'm surprised that rotating scanners are still used. It's been twenty years since Velodyne built their first one.

They're even older than that. SICK have been pointing laser range finders into spinning mirrors since about 1995 - albeit mostly for industrial safety systems which can be quite price-insensitive.

There's a few things to know about LIDAR to understand why spinning lasers make sense.

First of all, anything emitting a cone of light encounters "inverse square dropoff" - where moving twice as far away means you get a quarter of the light, per unit area. This is most visible with flash photography at night - but it also applies to LIDARs. And in an automotive application, ideally you want to be able to sense things 100m away. Illuminating a laser spot is much more practical than illuminating everything.

Secondly, whatever light source you use has to be eye-safe. And sure, IR has safety advantages over visible light here - but a light source bright enough to illuminate things at a 100m distance would be very hard to make safe, even with the advantages of IR. As a scanning laser never lingers in one point for long, it can safely be much more intense.

The third thing to know is whatever light source you're using, you're in competition with the sun. Sometimes the sun is low in the sky and directly dazzling your sensors. Other times it's illuminating the same things you want to illuminate. This means you can't make up for a weak light source and inverse-square dropoff with clever signal processing.

And finally, the makers of these cars envisage a future where every single vehicle on the road is using this technology. So there's also a risk of the reflected returns of two different vehicles interfering with one another. Even rotating LIDAR can be vulnerable to it, but flash LIDAR is particularly vulnerable.

Meanwhile, automotive companies aren't scared of moving parts. A car has loads of spinning parts already; they have mastered the art of making spinning things that can keep spinning for thousands of hours.