how to calculate consumption of a a 9w bulb

lovelyjubbly

I know this is really penny pinching, but times is hard, can anyone tell me how to calculate how much electricity a 9w low energy bulb uses, I have a light on all night every night as I usually have to get up in the night for the bathroom (too much information) the light goes on around 9pm as it is in a standard lamp in our sitting room and it is the only light we use in the evening, it then stays on till about 7.00am when i get up, now, I am on E7, so some hours are on cheap rate, but the majority are on standard rate 9.00pm till around 2.30am when our cheap rate kicks in, so what is the formula to work out how much it uses in an hour/evening? :huh:

A_fiend_for_life

1kWh = 1000Wh

1000Wh / 9W = 111 hours (the Watts cancel out)

about 10p or 12p for 111 hours for ordinary tariff. Not sure about E7.

lovelyjubbly

wow that was a quick reply fiend (hope you dont mind me calling you that)
thanks very much, I feel reasured that I am not spending too much on my night light!

amcluesent

Assume you tariff is 10p per KwH, then an 9W bulb would cost 0.09p per hour. Scale according to the tariff and number of hours the bulb is on for.

Even if left burning all night and day, an 9W bulb would cost £2.59 per quarter.

Fred_Bear_2

lovelyjubbly, here are the calculations you need. You did not say what your unit prices are but let's say 10p day rate and 4p night rate:
Day rate: 5.5 hours at 9 watts at 10p per Kwh: 5.5 x 9/1000 x 10 = 0.495p
Night rate: 4.5 hours at 9 watts at 4p per Kwh: 4.5 x 9/1000 x 4 = 0.162p
So total cost per night is 0.657p or just over half a p.
HTH