According to CJT :

I read what the others said, but I have a different suggestion.

It sounds to me like perhaps the neutral has become disconnected,
probably at the service entrance. Corrosion, perhaps?

A loose main neutral would result in some of the lights _brightening_,
or at least, _none_ of the lights in the house would retain normal
brightness. Secondly, the fact that the lights only dimly light up
when 240V circuits are on, is even stronger indication he's lost
a hot leg in the panel.

A $5+/- outlet tester that you could get at Lowe's/HD would quickly
tell you if I'm right (assuming you have outlets with a safety ground).

It's going to be as confusing as the behaviour of the lights. The
tester really needs to do voltage measurement. I'd recommend
testing things with a voltmeter inside the panel if the OP
felt comfortable with that.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.