In article , Tekkie® wrote:

I have a mercury vapor light that turns itself on/off intermittently at
night.

I called the electrical contractor that installed it and thought I just
needed the bulb replaced. The owners wife who answers the phone said it
could also be the ballast.

My experience is that over 90% of the time, the cause is the bulb
needing to be replaced.
--
- Don Klipstein )