As you might expect for a song contest held in the late seventies, Intervision didn’t allow its viewers to vote by text message. Instead, those watching at home had to turn their lights on when they liked a song and off when they didn’t, with data from the electricity network then being used to allocate points. The strange thing about this (well, one of the strange things) is that it’s a far more democratic system than the one used by Eurovision which, until 1997, relied solely on panels of music professionals for its judging. The light switch voting method isn’t perfect, of course; the results can only be estimated – and it does have the downside that, if you don’t like one of the songs, you have to listen to it in the dark.
https://blog.insureandgo.com/cultures-and-traditions/2014/05/intervision-song-contest-the-soviet-unions-answer-to-eurovision
Найдено по линку отсюда, в свою очередь, обнаруженному по этому линку.
У меня в детстве телевизора не было, так что я доподлинно не знаю, но что-то уж больно сомнительная история.