Maker Pro
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Loooong distance IR detection, and IR collimation


Rich Grise

Jan 1, 1970
Is an interesting topic I've never heard of or thought of before.

First, what is an Opticon?

Then, how does a (self-actuated) traffic-light work?

It contains a *camera* of some kind?

(I had imagined that it used some kind of sonar to tell when
a car appeared.)

It "photographs" in red? Or infra-red (heat)? Or what?

Interesting stuff -- please do elaborate a bit.

Well, an "Opticon", in this context, to the best of my knowledge, is a
photocell (electric eye) mounted up on the stoplight bracket, and
ambulances and fire trucks (and, presumably, the cops) have some secret
code that they flash through their windshield with a strobe - the Opticon
picks up that signal, and changes the cross-lights to red, and changes
the light for the emergency vehicle green. Some guy had decoded that code,
and was breezing through town, but presumably got caught because the
red-light cameras were timed to the moment when the light was
_supposed_ to have turned red - there was this car in the intersection,
and the "switch to red" signal had been overridden!

They caught the guy. :)

David said:
Then, how does a (self-actuated) traffic-light work?

It contains a *camera* of some kind?

The answer to this is "it depends". Some use coils embedded under the
road (often used at highway on-ramps in Long Island, for instance).

The more modern scheme is a camera in the traffic light that exploits
the highly reflective license plate on a car to detect if the
intersection is occupied.

I read something - here maybe - about a motorcyclist who was tired of
not triggering this type of detector. He put a strip of orange
reflector tape on his helmet and all was well.