How efficient are energy efficient light bulbs?

I think it's the law in the UK and they save energy and are therefore more eco-friendly but they are also kinda annoying because they are quite dull at first.

They use less energy to produce light, and thus save energy and help to save the environment through conserving electricity. The energy efficient light bulb applies fluorescent lighting technology...

From most energy efficient to least energy efficient:LED bulbs (relativly new) Fluorescent bulbs (normal "energy savings" bulbs) Halogen (used for high intensity lighting) Incandescent bulbs (regular...

Basically by reducing the input power for the same amount of light output. usually a gas like neon is lighted to emit photons.