[Madhatter]

They use 4 times as much energy to make.
The calculator doesn't work because it's a different sort of light, different wavelength. They give of more light, last longer and on average a low energy lamp will save you 131 pounds on your electricity bill over it's life. it will therefore reduce carbon emissions and green house gasses.
You can get low energy light bulbs for two quid, and two for two quid if morrisons has them on bogof.
Changing railway engines to use bio fuels would be megga expensive and as there isn't that many of them, wouldn't save as much as everyone changing to cfl's
What I do think though is that instead of a tax on normal bulbs, they should reduce or even zero rate cfl's.