I've just tested letting a Youtube video play on my M2 Macbook Air.
At 25% screen brightness, it uses around 4 Watt.
At 50%, around 6 Watt.
At 100%, around 11 Watt.
The person in question is unlikely to have a modern computer, but letting a video play all the time could technically still be using less power than the light.
That's insane to think about. Extrapolating down to 0% brightness means the actual compute required to manage the network connection and decrypt and render the video, plus anything the OS is doing in the background happens in maybe 2 watts?! With 2 watts you could power a fairly dim LED lightbulb or perform the equivalent of thousands(?) of man hours of hand computations.
At 25% screen brightness, it uses around 4 Watt.
At 50%, around 6 Watt.
At 100%, around 11 Watt.
The person in question is unlikely to have a modern computer, but letting a video play all the time could technically still be using less power than the light.