That's what I heard, too. But that's not "interefence effects from
electrical lights".

You are assuming that all interference would be on the screen
itself and none would be visual. Since flourescent and to some
extent incandescent lights blink (what is the persistance of an
incadescent light?) at 60 Hz, there is a strobing effect if there
are lights on in the room with the TV.

Incandescent lights have almost no flicker, due to the thermal inertia of
the filament. Fluorescent lighting was not common in living rooms at the
time the standards were set.