There are certain items we never like to spend money on. No one gets excited when it’s time to buy new washing powder and no one call their friends when they’ve just picked up some new dishcloths. At least I hope not. At the top of this things we begrudgingly have to buy list could well be light bulbs. Whilst I am not knocking Edison’s finest invention it’s always a bit of a pain when one goes and we have to spend hard earned cash getting a new one.
To make matters worse many new building now use spotlights. There are two issues with spotlights, one is that to illuminate a large room many more are needed. The second is that energy saving bulbs that fit spotlights are still relatively expensive and sometimes hard to source, which can be off putting for people looking to switch over to energy saving types.
I’ve recently moved into a rented flat with 10 GU10 type spotlights, none of which were energy saving. I was surprised at the high cost of energy saving bulbs (£6 each) but then I decided to do a little maths. They might cost more to buy but as they use less electricity they should save me money in the long term, right?
Most utility providers charge per kWh of energy used. Around 22.2 pence/kWh was taken from a large UK based utility provider. We can work out how much energy in kWh our bulbs use by multiplying the duration that they are used per month, the power of each bulb and the number of bulbs we have.
Say the lights are on for 45 hours a week (5 hours per weekday and 10 hours per day on the weekend)
That’s 45 x 4 = 180 hours a month. If you have 10 bulbs at 50 watts each then the total energy used per month is
180 hours x 50W x 10 bulbs = 90 kWh.
At 22.2 pence/kWh the price is 90 kWh x 22.2 pence/kWh = £19.98
If you were to change your light bulbs to energy saving ones then only 3W might be used per bulb. This makes the energy used and cost per month far smaller
180 hours x 3W x 10 bulbs = 5.4 kWh.
At the 22.2 pence/kWh the price is 5.4 kWh x 22.2 pence/kWh = £1.20
Of course the bulbs do cost more, ten bulbs will cost around £60, but that’s not to say they will not make a saving in the long run. Using the above formula we can work out how much the bulbs will cost over a period of months. The energy saving bulbs start off more expensive due to a higher initial cost, but as they are cheaper to run per month they soon start to make you savings.
As you can see from the graph after around 10 weeks the bulbs have paid for themselves. By the end the year (52 weeks) a total saving of £194 has been made. At a value of 0.544 kg of Carbon per Kwh of electricity used at home [1] changing over also stops 600 kg of Carbon being emitted each year which of course will help help stop global warming.
Saving money and helping the environment? Now that’s almost worth calling your friends about.
[1] Derfa 2009 figures at http://www.carbontrust.co.uk/cut-carbon-reduce-costs/calculate/carbon-footprinting/pages/conversion-factors.aspx [29/10/2010]
