If you're at all interested in self-driving cars, you've heard the term "lidar", which is a contraction of "light detection and ranging". It's been the stuff of experiments and prototypes, but is coming to showroom cars soon. Time to understand it.
Inside a lidar unit is one or more laser emitters and a corresponding set of laser detectors. The emitters send out a beam of laser light in the 905-nanometer spectrum range (infrared), and a matching set of laser detectors in the unit tries to pick up each beam coming back off of objects. This delicate dance happens in nanoseconds from a unit usually mounted on the roof of a moving car. As a result, only about 1,000 laser signals are detected for every billion emitted, but that's enough to build a "point cloud" of reflections that shows the shape, distance and trajectory of objects around the car.
That point cloud is different from what a car "sees" via other sensors like radar, cameras or ultrasound. Lidar is particularly good at sensing shapes in more detail than radar, and sensing depth better than cameras can. Radar, however, still excels at long range, low cost and the ability to see through weather. Cameras are better at "reading" sign text or lane markings that have a visual presence but very little physical relief.
If you've seen a lidar unit on a development vehicle, you probably noticed it was pretty large, sat up high, and was spinning. You just spotted most of lidar's pain points: Size, integration into bodywork and durability on the road.
Price is another big issue that dozens of lidar companies are working on. Lidar units have recently come down from hundreds of thousands of dollars to a few thousand dollars apiece, but that's still too much to profitably blend into the $34,000 sale price of the average car.
People often ask about the safety of cars roaming the roads with "spinning laser guns" spraying the sidewalks and buildings around them. That is a real concern, and is why current lidar using 905 nm lasers are limited to very low power and limited exposure times, which a rotating lidar handles by never stopping in one position. Some lidar makers advocate moving to a higher lidar laser wavelength of 1,550 nm, which is said to be harmless to human retinas, allowing lidar power and range to be increased.
That's a long list of things to be solved by the time lidar is called upon at scale to give sight to the next wave of autonomous cars in 2020 or 2021.