What year did the infomercials start and "dead air" end?

A yahoo-er said there use to be " dead air" on TV at night. I was born in the 80's and remember that a few channels may have had "dead air" and little lines on the TV at night... though I'm not sure if it was all of them or not.. I doubt it. What year did the informercials or TV... show more A yahoo-er said there use to be " dead air" on TV at night.

I was born in the 80's and remember that a few channels may have had "dead air" and little lines on the TV at night... though I'm not sure if it was all of them or not.. I doubt it.

What year did the informercials or TV all night start?

Was there ever complete dead air on all channels and what year did it end?
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