Can you really save nearly £50 with a single light bulb?

Yes! Each low-energy bulb you install will save you money in energy costs. And with some bulbs, the savings can be close to £50. (In fact, that's a cautious figure: the Energy Saving Trust says £100 savings are possible.)

An example calculation:

• A 100W-equivalent low-energy bulb (such as this one) consumes 18W of power and lasts for around 6000 hours of use. In that time, the overall running cost will be around £10 in electricity (6000 hours * 0.018kW * £0.09p/kWh), plus £1 for the bulb itself. Total cost = £11

• A 100W incadescent bulb lasts around 1000 hours. So to produce 6000 hours of light you'd get through six bulbs, at around 50p each, and spend a massive £54 on electricity (6000 hours * 0.1kW * £0.09p/kWh). Total cost = £57

That's a saving of £46 – a return of 4600% on your £1 investment in just a few years. Rather better than premium bonds!