Thankfully I live about 2 miles from the nearest street lights and at night time it gets really dark here. The idea of automatic path lights is appealing.
I have an idea, what do you think of it:
All the lights can be solar powered or run from low voltage battery or mains adapter. Each unit utilises an LED as the light source and also has an infra-red LED and an infra-red sensor in it. The infra-red LEDs are aimed at the next unit along the path, crossing over the path in zig-zag or straight across directions. The IR LEDs flash at about 2Hz rate (twice a second) keeping the current drain very low. The sensor on the next unit downline picks up the flash and uses it to reset an electronic timer. If the timer goes beyond half a second (it was not reset) it switches the lighting LED on for say 30 seconds then switches it off again and goes back to monitoring the flashes.
The idea is that as soon as one of the IR beams is broken, the next light along the path, the one receiving the beam, turns on for a while. There's a need for a flash generator at the end of the path to trigger the first unit of course and the beam must be broken for long enough by someone passing through it.
In my mind I see a cheap microcontroller chip doing all the flash generating and timing functions. Without properly pricing it, I'm guessing the cost of all the parts excluding the PV (if solar powered) to be around 5 UK pounds ($10 US).
I'll add it to my project list.
Brian.