A long time ago, when I was a much younger person, one of the ways I knew I had stayed up way too late watching TV, was when the show ended, I’d hear the Canadian national anthem, overlaid with images of this great nation. Once the anthem was done, there would be a test pattern shown, and the channel would be off-air for many hours until the morning, when programming would resume.
For some of you younger viewers, it may come as a surprise to you that television did not broadcast 24 hours a day. Depending on the channel or the year, sometime after midnight, channels would just stop broadcasting programs. The test pattern was shown so that you could adjust your televisions at home (and also not show static for several hours).
There was no Internet or streaming services, so once it go too late and all the channels went off-air, there was very little in the way of entertainment to watch on TV. In the time before VHS players, you couldn’t even pop in a tape to keep yourself occupied. Those were simpler and obviously more boring times.
In the present day, broadcast channels really don’t go off-air daily anymore. There’s a lot of automation going on, so you can broadcast programs around the clock with very little human input. It probably makes more financial sense to broadcast throughout the night as well, as you can sell ads for more hours. Also, I’m not sure who used test patterns to calibrate their TVs back then but I’m sure no one needs to do that now. To be clear, even modern TVs need to be calibrated but I don’t think people are relying on a TV channel to help them with that.
It used to be you could rely on the test pattern to tell you go to sleep. Now you don’t have to sleep ever!