Modern cars increasingly have automatic lights.

So users assume that the car is going to turn the lights on for them.

However in daylight in fog the automatic system doesn't work (as its not dark enough).

How do you stop people driving along in fog thinking that their lights are on ?

(This is an example of the Paradox of Automation BTW )

  • The trivial solution would be to remove automatic lights (because automation doesn't work if the operator still has to redo every single decision and do this in real time). But I assume you wish to keep the advantage of automation in non-foggy environments, in which case the logical next question would be whether the automated system could possibly distinguish this "not sure whether you need lights" state from unquestionable daylight. Commented Feb 23, 2019 at 17:44
  • So basically add more tech, or take some away. It's an interesting dilemma when adding tech solves one problem, yet generates another one.
    – PhillipW
    Commented Feb 23, 2019 at 19:21
  • Comment 1: Is this a realistic problem? Most cars come with daytime running lights that are not automated. Rather, turning on the car turns on the lights. It is a legal requirement in some countries. Commented Feb 27, 2019 at 16:50
  • Comment 2: Assuming the problem is realistic, there is no indication to the driver lights are needed in the fog. Otherwise, the driver could not see well enough to drive and would turn the lights on. The benefit of turning on the lights is for other drivers/pedestrians rather than the driver operating the car. This makes the question more interesting, i.e., how do you get a driver to do something with no direct benefit to her/himself but for the benefit of others? Commented Feb 27, 2019 at 16:53
  • You correctly point out that daylight running lights will be on - but these are not as bright as having dipped main beams on.
    – PhillipW
    Commented Feb 28, 2019 at 0:34

1 Answer 1


You could use an Optical Fog Sensor (OFS). When the car's microcontroller detects that the quantity of fog has crossed a threshold, it can instruct the fog lamps to be turned on.

How OFS works - backscatter technique

A narrow beam of red laser light comes out of an opening on the front. A detector behind a lens in another opening is sensitive for incoming laser light in a narrow lobe that overlaps the transmitter beam.

If there are fog particles in the overlap zone light will be scattered back and reach the detector causing a signal on the sensor raw signal output. The sensitive zone is located about 30 cm ahead of the sensor and its volume is less than 1 cubic centimetre.

To know more about OFS: http://opticalsensors.se/ofs.html

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