How much energy does a nightlight consume and how much does it cost to run it all day?

It depends if you use a newer LED, or older incandescent bulb style.


The old bulb style (still popular, and usually cheaper to buy) use about 7 watts.
If you use that for 8 hours, you would use 56 watt-hours. For a year that would be about 20.5 kWh (kilowatt-hour).


An LED style light may be 1/4 watt, which works out to be .73 kWh. per year.


How much that cost depends on where you live, and what rate you pay. 10 cents an kWh is a reasonable approximation for the United States. At that rate, the Bulb light would cost about $2 a year, and the LED would cost 7 cents.


If you leave the light on all the time (in a dark bathroom) triple these numbers. The bulb style would be $6 and the LED about 20 cents. You can see that although the LED light is more expensive up front, it could pay for itself in energy savings in about a year. But neither light will cost that much to run.

<<>>

NOT MUCH, I would say A penny or less A day.

....a different (cost and environmental) perspective - although the answers above are correct, for small devices using cost always gives answers that seem tiny. For 2 reasons we should get away from this approach: (1) lots and lots of small items add up to a lot; individually they might be small but if that means we ignore all small costs they soon add up. (2) think carbon - 20kWhrs is about 20kg of carbon dioxide (say 45 lb) a year - that's about 13 cubic metres of greenhouse gas just for a nightlight!