the idea of using very high-value resistors for a zero x ing sensor=20
is only really a danger if
A.The PCB tracks are not upto spec for mains voltages and currents
especially taking into account the often soggy conditions inside outdoor =

enclosures,design would need to take into account creep at mains =
voltage.

B.the low voltage side of the circuit aren't double insulated  from the =
user
by sealed cases and PLASTIC controls (pots,switches,etc.)as well as=20
a good earth connection

C. the mains supply isn't protected by an RCCD circuit breaker.

Another (stone-age) method of bulb failure detection is by simply =
wrapping the feed=20
wire around a reed relay whose contacts feed the trigger (fail detect)
circuit.This simple scheme is used on cars and trailer bulb warning =
units
that i've pulled to bits....Well you HAVE to, dont you!Learn from other =
peoples mistakes.
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