Any Excel gurus out there?

[shiftkeying]

I'm making a spreadsheet comparing overall costs of CFL light bulbs with those of tungsten bulbs. Working out the running costs is easy, what I'm struggling with is factoring in the capital costs of the bulbs. The tungsten bulbs last for, say, 1000 hours and cost 50p each and the CFLs last 8000 hours and cost £5 each. What I want to do is add these costs as a discrete value every 1000 and 8000 hours. Is there a simple way to do this??

[Been Accounting]

Divide the capital cost by the life-on-wing = capital cost per hour
Add this to the cost of power per hour

Or is it more complicated than this?

[BOFH]

Judging by your figures, I'd say buy tungsten!

Been Accounting is right - I'd do something like this:
IF(B1 > 0 THEN B1 = B1 * <proportion>, {else} B1 = {cost of bulb})

.. and copy it down the range. The whole idea is that you are decrementing until you hit zero, then you bounce up again. Plotted against time, you should see eight bounces on the tungsten side for every CFL bounce.

BOFH