RS LOZWORTH is 100% totally correct.
The lights are working EXACTLY AS HE SAYS.
The sensors are not CAPABLE OF SEEING LIGHT, they are MICROWAVE SENSORS on temp lights, they are tested with aboard run down a string towards them and they must react at the correct distance.
They do indeed go ALL RED, when they have detected no motion for a set period of time, then when motionis detected by MICROWAVE not LIGHT they run the CLEAR TIME first then go down to green on the appropriate side with the camera that has detected.
This is why some refuse to budge when a camera goes wrong on end will stay green whilst the other stays red.
Normal or permanent lights operate as he says, with induction loops BURIED IN THE ROAD about 10-20 feet before a junction, have a look easily sptted as they are odd angle lines covered over with smooth tar when installed.
Temp lights, roadworks etc, can have thier timings individually adjusted to suit each road for green time, clear time(all red) and red time.
There is a host of legal criteria for setting out temp lights, a lot not adhered to.
If ANY light in the world were activated by light, what di you think would happen in daylight as the sun is a little bit brighter than the average car headlight.
tabetha
ps good explanation by RS LOZWORTH