> I don't know about CFLs, but our house has several "energy saving" 
> lighting units. The problem is, there's a 20 minute delay between turning 
> them on and being able to see where you're going...

Yup, and not having studied them carefully, I hear they make a slight 
buzzing noise which can be annoying in a quiet room (eg while trying to 
read).

> LEDs are indeed efficient, but the main problems currently seem to be 
> making "white" light with them,

There's no problem with making white light, the most efficient way is just 
to put a mixture of different coloured LEDs in one "lamp" to give whatever 
white temperature you want.  The other way is to put a yellow phosphor 
infront of a blue LED, but that's not as efficient electrically (it means 
you can get white from a single LED though).

> and illuminating large areas.

The biggest problem is keeping the LED temperature low enough during use, 
the designs I've seen have been mainly heat sink, but they seem to have 
overcome that for 60W and 100W equivalent bulbs:

http://www.metaefficient.com/leds/led-light-bulbs.html

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