Is it true?

When you're at a traffic light at night and noone else is around is it true that by flashing your lights at them they'll change colour as in the lights not the pole . my dad generally does it and on occasion it 'works' but is this coincidence I thought they were timed.

In some regions they have devices on the traffic lights that let emergency vehicles to change the lights at an intersection to let them to stop cross traffic. there's typically a strobe light on the firetruck, ambulance, etc., that these devices detect. I doubt your dad can flash his lights at the same speed as a strobe. What he's most likely doing is watching the yellow light for the cross traffic and flashing his lights to make you think he's the power to change traffic signals. Sorry if that ruins the illusion for you.

They are timed or weight activated. there aren't sensors or anything to see lights, or else you'd have big backups due to constant changing of lights. it is just a coincidence.

Your dad is pulling your leg. He can be watching the lights on the cross traffic light or trying to time the sensor buried under the road to make you think he's really making a difference by flashing his lights.

If he really thinks his flashing has an effect, I'd avoid taking investment advice from your dad.

well some lights, not many, have sensors that are supposed to detect emergency lights on fire trucks, ambulances and such. they'll really change depending on the sensor being tripped, but they usually can not be fooled by flashing headlights once your stopped. I do recall one intersection in a adjoining town where it could work but only if you flashed your lights at some point while driving down the hill toward the stop light.

My guess is either your dad heard about it once and now blindly believes that all light operate this way or he's playing with you.

The odds of you living in a place where they all function like that's about 0.