How long until an energy efficient bulb saves its purchase price in energy costs?

Question

If I replace the 22 lightbulbs in my house with energy efficient ones it will cost about £130.How long will it take for them to save me money overall,taking into account the purchase price?

Answer 1

It depends on a lot of things.
1) How much light does the new bulb make?
2) How much does the new bulb cost?
3) How much electricity does the new bulb use?
4) How long before the new bulb burns out?
5) How much light did the old bulb make?
6) How much did the old bulb cost?
7) How much electricity did the old bulb use?
8) How long before the old bulb burns out?
9) How long is the light on during the year?
10) What do you pay for electricity?

To make things easy, let us assume you found a new energy saving bulb that makes the same amount of light as your old 60 watt bulb, but it uses only 13 watts. You are saving 60-13=47 watts. Electricity is sold in units of kilowatt hours, which is the amount of energy delivered if you use 1,000 watts for one hour. So your 13 watt bulb is saving 60-13=47 watts, which translates to a savings of 47 kilowatt hours for every 1,000 hours the bulb is on. If you pay $0.12 per kilowatt hour, you are saving 47*$0.12=$5.64 every 1,000 hours the light is on. (Excuse the American $, I live in Texas). If the light is on 1,000 hours a year, you will save $5.64 per bulb per year. If the 13 watt bulb costs $5.64 more than the old bulb, you will recoup the cost in one year. If you have the light on more than 1,000 hours a year, or your electricity is more expensive than $0.12, or the new bulb does not cost as much as $5.64 more than the old bulb, then you recoup your cost faster. The number of watts the bulb uses is usually printed on the bulb or on the package it came in. Your electricity cost is on your electric bill. The number of hours a year you have the light on will have to be estimated or even timed by you. And that is just the simplest case. To make it more accurate you need to include how long the bulb lasts and how much light the new and old bulbs really make. If the 13 watt bulb only makes half the light of the old bulb, you should attribute only half of the saving to new bulb. The amount of light a bulb makes, usually specified in lumens, is sometimes printed on the package and sometimes not. But is probably enough to just judge by eye if the light is about the same or not.

So it is not a simple thing to determine at all!

Answer 2

It depends. You have given the cost of the bulbs you will install. What you need to do is subtract the wattage of the new bulbs from the existing bulbs, multipy that by the hours that they are on per day, multiply that by the cost of electricity. This gives you the monetary savings per day. Divide that into the cost, and that will yield the number of days to payback your investment.
Here in Colorado, a bulb that is left on four hours a day pays for itself in two years. Energy efficient bulbs usually payback about five times their cost. The fewer hoursper day that you use them, the longer they last!

Answer 3

Very difficult to say with fluctuating electric prices and differing Osage of each bulb. But according to The National Energy Foundation (see ref), a bulb with an average usage of three hours a day would pay for itself in savings in under a year, whereas a bulb with an average usage of one hour a day would take about 2.5 years to pay for itself in savings.

Answer 4

in the states around me it costs $0.03 per 24 hr day to run a 100 watt light bulb, and the equivalent of that a 17 watt florescent costs $0.005 per 24 hr day to run

the 100 watt bulb costs roughly $0.20 and the 17 watt florescent costs roughly $2.00 for a difference of $1.80

based on that $2.00 - $0.20 = $1.80
and cost to run .03 - .005 = .025
take the 1.8 / .025 = 72 days to hit the break even point that is if i run the bulb 24hrs a day 7 days a week
or that would be 1728 hrs of usage
but then in that time frame would burn up 2 bulbs
so refactor that
2 - .40 = 1.6
1.6 / .025 = 64 days x 24 = 1536 usage hours
so from there on out you are saving money
on average the say you save about $37 per florescent bulb over the course of their life

Answer 5

Hard to say really. Some energy efficient bulbs can last up to seven years.

Answer 6

they cost 5 or 6 times as much.

but last 8-10 longer

so they will save you money about half way through their life span.

Answer 7

It depends on how long you keep them lit each day the cost of poewer there. It should be simple arithemtic.

Answer 8

3 years - read it in the paper a couple of weeks ago.