The modern LED bulbs you can get must convert the standard household supply (for example $240\text{v AC}$ in the UK) into a DC supply at a lower voltage (usually $12\text{v DC}$ I think) for the LED array. This is done on a per-bulb basis.

Does this waste much power in the conversion? If all of your bulbs are LED bulbs, would it make sense instead to have a $12\text{v DC}$ circuit for lighting around the whole house and LED bulbs without the per-bulb conversion?