Of the energy used by incandescent light bulbs, 95% go into heat and only a very small part goes actually into lighting. Low-energy light bulbs are much more efficient. A 20 watt low-energy light bulb produces the same light as a 100 watt conventional one. The table below compares incandescent light bulbs and low-energy ones.
low-energy light bulbs are more expensive to buy but have much longer lifetimes than incandescent light bulbs.