How much to run a low energy light blub for 12 hours?

MrsE_2

How much to run a low energy light blub for 12 hours?

The one that replicates 60 watts

HappyMJ

About 1 penny.

penrhyn

It depends on the wattage of your lamp and the price you pay for your electricity.

jd87

Yeah about 1 penny is a good estimate. Assuming an 8 watt bulb and a price of 12 pence per unit:

One unit is 1000 watts for one hour.

(8/1000) x 12p x 12 hours = 1.15 pence

Ben84

MrsE wrote: »

How much to run a low energy light blub for 12 hours?

The one that replicates 60 watts

It depends on the wattage of the energy saver you're using and the cost of electric, but once you've found these two details it's just a few calculations to answer the question for how much any appliance costs to use. The important points are in understanding the units here as when you do this the calculations needed become straightforward in most cases.

All appliances have an energy rating in watts printed on them, which in the units of joules per second, but is basically just the rate of energy consumption at any moment in time. It's analogous to turning on a tap and measuring the water in litres per second. You know the rate of flow, but to turn rate in to quantity requires a value for time to be included. This is why electric is billed in units of pence per kilo watt hour (kWh), which is the cost in pence of continuously consuming 1000 watts for an hour.

To take an example from my house, I have a 42w halogen bulb that replaced a 60w bulb in my table lamp, so over 12 hours it will use 12h x 42w = 504wh (wh is watt hours) of electric.

Electric is normally billed in units of 1000 watt over an hour (kWh), so I divide 504w by 1000 to find the number of kWh used, which is 0.504 kWh.

To turn this in to pence you need to bring in the cost in pence per kWh provided by the electric company, which if used right will cancel the kWh and leave a value in just pence. So, multiply the cost of electric in kWh by the number of kWh used. I pay about 8.9p for a kWh so for 12 hours my table lamp costs 0.504 kWh X 8.9p / kWh = 4.49p. The kWh has cancelled out as there's one on the top and bottom of the equation (sorry - it's not so easy to show in the text style here) and we're left with a value in just pence for the amount of time (12 hour) the lamp has been used for.

My 42w halogen is just one type of energy saver, there are various other types, including fluorescent bulbs that are likely to be more economical at about 11-12w. Hopefully I've explained well and you could do the calculation again to suit whatever bulb you're thinking of with your own cost of electric to get the exact figure.