At first glance, the number appears to be big. But when you put it into a context, you might arrive at a different conclusion.
Originally Posted by sanking
12 tubes at 40 watts = 480 watts
Assuming an 8-hour working session, that becomes 3840 watt-hours, or 3.84 kilowatt-hours.
Where I live, the local bandits (the utility) charge about 17 cents per kilowatt hour. So the energy cost for an 8-hour working session would be about 65.3 cents.
The B&S combo kit sells for about $150 and is supposed to be enough to produce about 20 8x10s. An 8x10 sheet of COT320 costs about $1. So the materials that go into one 8x10 print (regardless of good or bad) cost about $8.50.
Let's assume that you are really industrious and can produce 16 prints during that session. That means that the energy component of per-print cost associated with leaving the lights on throughout the session is about 4 cents.
When you look at it this way, the energy cost doesn't seem so significant.