"light bulbs began to go off"

[AAllan at AOL.COM]

I noted this expression in the comment of a Boston doctor on NPR's Morning
Edition January 19, meaning that a bright idea came along. But lights going off
(as opposed to on) doesn't make sense to me.

Found half a dozen other examples by googling, including:

 <<"The loss of speech, the melancholy, the behavioral problems that go along
with mercury toxicity were identical to what Will was exhibiting and that's
when I guess the light bulb went off," Redwood said.

 The light bulbs began to go off in the minds of other Georgia parents, as
well, whose children were also diagnosed with autism.>>

There are almost 14,000 Google hits for "light bulb went off," like this one:

<<The infamous light bulb went off... I finally figured out two-handed
knitting for the 2 color socks!!! I really ...>>

I'm old enough to think this metaphor comes from flash bulbs going off. But
there are few Google examples of that.

- Allan Metcalf