A nugget of truth which Scott35 mentions, and which is also described in the Lighting Design Lab article:
_Starting_ a lamp can _cost_ as much as running that lamp for a significant period of time.
Starting a lamp will eat into its useful life. Lamps take energy to produce, transport, install, and dispose of. So anything that shortens the life of the lamp is using up some of that 'latent' energy.
Rather than calculating the number of kWh is used up simply to have the lamp, it generally makes more sense to talk about the monetary cost of having that lamp. The lamp itself might cost $1 or $2; but you also have to pay the labor for relamping, as well as costs for disposal, so for a quick back of the napkin calculation, it is fair to say that a lamp costs $10.
Depending upon the technology of the lamp and ballast, you will get anything from 5000 to 200000 starts per lamp (the 200000 is claimed by a manufacturer for a modern and expensive program start ballast, and I'll belive it when I see it.) Say you get 10000 starts per lamp...this says that starting the lamp costs $0.001.
Say the lamp uses 40W after you account for ballast efficiency, and electricity costs $0.10 per kWh. This tells us that it costs $0.004 per hour to run that lamp.
With these assumptions, starting a lamp _costs_ the same as running it for 15 minutes.
I had to pull a bunch of numbers out of my left ear, and costs in a particular situation may be vastly different (especially if you have the program start ballasts), but the cost of starting a lamp is _not_ negligible, even if the power usage is.
-Jon
