Graeme wrote:

An LED night light burns 0.5w, so 1/120th the cost,
or 16 pence - is that right???

A rule of thumb is £1/year per watt that's on 24x7, it's probably
slightly under given price rises in recent years.

So a 0.5W light would be 50p/year if left on 24h/day, so 16p for 8h/day
is about right.