An outside light is tripping the breaker, which one is it of six?

[Chris Wilson]

UK 240V 50Hz mains. 6 outdoor lights on a light dependent sensor so they all come on at dusk and go off at dawn. Recently they haven't been coming on. Distribution box shows the breaker for them has tripped out. I rest it today and when it grew dusk it tripped again. The main RCD is not tripping, so I suspect a shorted bulb or holder. Some are LED, some are whatever the older bulbs were that took ages to come up to full brightness when they aged. Is there any ingenious way to find the offending one, given they only get power at dusk and the sensor was put inaccessibly to other than a cat burglar at some dizzying height? Thanks.

[sokoloff]

Day 1:
I would unscrew/remove 4 of them.

Day 2 if that does not trip:
Restore 2 of them. Troubleshooting from here is probably obvious.

Day 2 if that still trips:
Remove 1 more.

Day 3 if that still trips:
Remove the last one.

That should get you the fault (assuming a single fault) inside of 3 trials.
The reason I'd start by killing 4 is you're not sure it's a bulb that's bad and 3 takes just as many days to check anyway.

[bdunham7]

Are the bulbs accessible?  If so, take them all out and try them in a lamp socket one at a time. FWIW, I personally have never seen an Edison-base bulb short or trip a breaker.

[Brumby]

Keep in mind, any part of the circuit could cause the tripping, not just the globes or holders.  I presume the tripping is from overload ... you don't have these on an earth leakage/RCD breaker, do you?

FWIW, I personally have never seen an Edison-base bulb short or trip a breaker.

My experience also.