Standard light bulbs use up to around 4 times the power(electricity) that low energy bulbs use. So if you change to low energy ones that will give a big saving on the electricity you use on lighting.
Low energy bulbs are more expensive to buy but last much much longer. You will definitely make a cost saving over the life time of the bulb as well as using far less energy.(and CO2 emissions)
Low energy eqvuivalent(watts)
Low energy bulbs are basically mini fluorescent tubes, so the light you get from them is like a fluorescent tube. Some people don't like the light they make and also complain that they aren't as bright. These factors will vary with the cost and quality you choose. Try a few different types and see what you think.
The cost saving you will make depends on several factors. How much the bulbs cost, how long they last, how much less electricity they use, and how much time you use them per day. Generally you get what you pay for so check the bulb life versus cost.
To compare your own bulbs for cost and energy saving use my bulb comparator click here It also shows how much CO2 you'll save with energy saving ones
Below are a few examples of common bulbs compared with a low energy equivavlent.
GU10 fitting Mains Halogen
GU10 Megaman Mains Compact Fluorescent
NB if you're replacing a standard bulb with a low energy one check that the new bulb will fit into your particular light fitting. Most will but some don't.
GLS Standard bayonet cap bulb
GLS Compact fluorescent
Standard type Standard candle bulb bayonet cap
Energy saving Megaman ultra compact candle CFL
Standard type MR16 12 volt Dichroic
Energy saving MR16 12 volt Philips Masterline Energy saver