[isthisnametaken]

Indeed. I used to have some old bayonet fitting plugs from my grandparents' house.

One was even in its original box, which showed an illustration of woman ironing using an electric iron powered by a cable hanging from the light fitting.

[teddyh]

Electricity used to be priced differently for lights versus other uses (lights were much cheaper), so these product were essentially DRM-bypassing tools.

[tialaramex]

In what era are you claiming this?

The UK does have "Economy 7" tariffs which are a much simplified off-peak discount intended primarily for storage heating. The idea is, we provide a meter which knows what time it is, for 7 hours each night (when generally power usage is lower) you are charged less per kWh than the other 21 hours per day.

If you keep a Tokyo schedule but live in Yorkshire then this might work for you, but the primary use case was electric storage heating, during the night cheap electricity heats some bricks in a box, during the day you let the heat out of the box to keep your home warm, next night the bricks are re-heated. It's annoying because weather is hard to predict, if you wake up to an unexpected blizzard, too bad, you will freeze or need to use an "immediate" heating source that's very expensive, alternatively if you predict the blizzard but wake to find it's sunny and mild, now your home is 25°C and you feel like an idiot.

I'm not aware of it ever being the case that some household circuits were charged differently in order to make lighting cheaper and it seems unlikely this would be effective. Electric lighting was a huge winner because it's both more convenient and cheaper to use than gas (or worse oil) lamps so an incentive seems unnecessary.