If you were offered an investment with a guaranteed return of 900% a year or 10,000% over its lifetime, with no tax to pay, and which had a positive impact on the world, you would snap it up, right? Well this is the sort of return you can get by installing low energy lighting inside and outside your home.

Let's look at some of the figures. Energy saving bulbs now cost from around £1 each. If you replace a bulb that you use for around 3 hours a night, then you save about £9 a year on your annual electricity bill. Because they last much longer, according to the Energy Saving Trust each low energy light bulb can save you up to £100 in electricity bills over its lifetime. If you add up all the light bulbs and fittings in your house, this adds up a surprisingly large saving.

Plus the benefits aren't only financial. Something as simple as using low energy bulbs can have a big impact on your personal contribution to Climate Change, by reducing the carbon dioxide emissions you are responsible for. Each bulb on its own will save up to half a tonne over its lifetime. If you replace 10 old-style bulbs in your house that you use for 2 hours a day with low energy bulbs, you will save around a quarter tonne of carbon dioxide each year.

Finally, low energy light bulbs save you time and effort. Because they last around 10 times longer than normal bulbs, when you switch to low energy bulbs you won't have to get the ladder out so often to replace bulbs that have blown.

So why isn't everyone making the change to low energy bulbs? Sadly too many of us are creatures of habit, and just carry on buying the same bad bulbs we always have. But now with the wide range on offer, and recent developments which have made low energy bulbs perform just as well as old-style bulbs, it makes sense to change all your bulbs straight away.

It does take a little effort to make the switch at first. First you have to go round your house and write down a list of the bulbs you currently use - including wattage (60w, 100w etc.), type of fixture (screw, bayonet etc), size and colour (e.g. are they toned?)

Next you have to work out the wattage for a low energy bulb that matches the wattage of your current bulbs (for example a 20 watt low energy bulb gives off the same light as a 100 watt old-style bulb). You can find simple tables that can help you do this on the Internet at sites like downwithco2.com.

Once you have worked out the bulbs you need to buy, you can then go shopping. There are many retailers of low energy bulbs on the Internet, or now they are commonly available in supermarkets or hardware stores.

Plus you can also save a lot of money by installing more energy efficient lighting outdoors. Just a few outdoor lights left on each night can double your household lighting bill and your greenhouse gas emissions. The best solution is to fit daylight and movement sensors so outdoor lights switch on when they're needed, but don't waste electricity. This also improves your home's security, as you can tell when someone is approaching the house.

For outdoor lights that must stay on for long periods, use energy efficient, compact fluorescent or LED lamps and choose the lowest wattage lamp that gives enough light. In the garden, you can now buy solar powered garden lights that use no mains electricity and so produce no emissions when used. Plus you don't need to wire up your garden to get lighting.

So now you have seen all the benefits of low energy lighting, it really does make sense to make the switch as soon as you can.