"mike" wrote in message
...
I've just fitted an exterior light with dusk-to-dawn sensor which
specifies an E27 11W ES lamp.

Bought E27 11W ES and then discovered it says not to be used with dusk-
to-dawn sensors.

Put lamp in anyway, and it works.

Why wouldn't it work and am I shortening the life of the lamp by using
it with a d2d?

Some D2D sensors are just light dependent resistors and they effectively
lower the voltage on the lamp when its bright.
This is a no no with CFL.

Better D2D sensors are proper switches.

You can spot the cheap nasty ones at dusk/dawn as the lamp dims and flickers
even with tungsten bulbs.