[oil pan 4]

If you have halogen work lights do what I do and get rough service replacements.
I was replacing my 150w motion detector halogen lamp every 2 or 3 months, then I put in a 100w rough service lamp and have not changed the lamp in 3 years.
On a side note I recommend installing a timer on halogen work lights. It will save power and reduce fire hazard.

Longevity is most definitely a part of efficiency. Having something fail, having to toss it and buy a new one of something definitely effects operating cost.
For example, LEDs loose efficiency if they are ran too cold, but the cold doesn't kill them, so they last just about forever.

The only disadvantage I can think of is your led never burns out, so you keep using say 60lumen per volt amp lights even as 150+ lumen LEDs come available, because your old ones just won't die.
But it's going to be a while before high intensity high efficiency compact white LEDs are available.
To get a lot of light from an LED and have it be highly efficient the LED pretty much needs to be its own fixture, that way you can have a huge array of low power LEDs working together to make a lot of light.
The best efficiency is had when you are running less than 10ma across your PN junction.
Run more than that and quantum physics starts cutting into efficiency.