Are you curious to see how long it takes for a CFL bulb to pay for itself. I finally did the calculation, for different wattages, using PG&E rates for Jan/Feb. Turns out it's a pretty good deal. PG&E has tiered rates for those that use more electricity, ranging from $0.11 to $0.47 per KwH. From the PG&E rate website:
Tier 1 (Baseline) Jan/Feb PG&E rates
Tier 2 (101-130% of baseline)
Tier 3 (131-200% of baseline)
Tier 4 (201-300% of baseline)
Tier 5 (Over 300% of baseline)
tier 1 elec = $0.11877 per KwH These are the prices that PG&E is charging at the moment.
tier 2 elec = $0.13502 They'll likely change over time (go up) but maybe not a lot.
tier 3 elec = $0.27572 If you're in a different state, you'll have to look at your bill.
tier 4 elec = $0.40577 Baseline varies, depending on where you are, and the
tier 5 elec = $0.47393 amount of electricity a frugal user would be expected to use.
avg $0.18471 *** EG, if you live in a hot area, they allow more for A/C use.
In the tables below, it shows how many hours it takes to recover $1 when you replace an incandescent bulb with a Compact Fluorescent bulb. If you shop carefully, in the PG&E area, you should be able to find CFL bulbs for a dollar. When I was out of state, they were generally around $6 each. If that applies to you, you'll have to multiply the hours by 6. Before I'd done this, I was pretty sure that the payback would be fairly quick, so I've already replace many bulbs. However, when I did these calculations, I was surprised at how quick the payback was. Monetarily, it really is worth throwing out all my good incandescent bulbs, and replacing them. For each entry, it indicates what wattage bulb is being replace with what, the difference in watts, then calculates the number of hours to save $1, depending on what tier user you are. It's worthy of note that when you replace a bulb, the difference in electricity cost is at the top end of what you're paying, not the average.
ALSO, when you're replacing bulbs, there's a couple things to watch. The 100 watt equivalent (23 watt bulbs) are a bit bigger, so you have to make sure they fit. HOWEVER, CFL bulbs generate much less heat, so i've put a couple 23 watt CFL bulbs in fixtures that say 60 watt max, because I really needed more light to work by. Okay, enough preaching, on to how long does it take for a bulb to pay for itself.
Replace a 60w with a 17w CFL, save 43 w/h
1000/43 = 23.26 hours to save 1kw
tier 1 elec = 23.26/.11877 = 196 hours to save $1
tier 2 elec = 23.26/.13502 = 172
tier 3 elec = 23.26/.27572 = 84
tier 4 elec = 23.26/.40577 = 57
tier 5 elec = 23.26/.47393 = 49
Replace a 60w with a 23w CFL, save 37 w/h
1000/37 = 27 hours to save 1kw
tier 1 elec = 27/.11877 = 227 hours to save $1
tier 2 elec = 27/.13502 = 200
tier 3 elec = 27/.27572 = 98
tier 4 elec = 27/.40577 = 67
tier 5 elec = 27/.47393 = 57
Replace a 100w with a 23w CFL, save 77 w/h
1000/77 = 13 hours to save 1kw
tier 1 elec = 13/.11877 = 110 hours to save $1
tier 2 elec = 13/.13502 = 96
tier 3 elec = 13/.27572 = 47
tier 4 elec = 13/.40577 = 32
tier 5 elec = 13/.47393 = 27.5
Replace a 75w with a 23w CFL, save 52 w/h
1000/52 = 19.23 hours to save 1kw
tier 1 elec = 19.23/.11877 = 162 hours to save $1
tier 2 elec = 19.23/.13502 = 142
tier 3 elec = 19.23/.27572 = 70
tier 4 elec = 19.23/.40577 = 47
tier 5 elec = 19.23/.47393 = 41
Replace a 75w with a 17w CFL, save 58 w/h
1000/58 = 17.24 hours to save 1kw
tier 1 elec = 17.24/.11877 = 145 hours to save $1
tier 2 elec = 17.24/.13502 = 128
tier 3 elec = 17.24/.27572 = 63
tier 4 elec = 17.24/.40577 = 43
tier 5 elec = 17.24/.47393 = 36
Replace a 25w with a 09w CFL, save 16 w/h **
1000/16 = 62.5 hours to save 1kw
tier 1 elec = 62.5/.11877 = 526 hours to save $1
tier 2 elec = 62.5/.13502 = 463
tier 3 elec = 62.5/.27572 = 227
tier 4 elec = 62.5/.40577 = 154
tier 5 elec = 62.5/.47393 = 132
Replace a 120w with a 23w CFL, save 97 w/h *
1000/97 = 10.31 hours to save 1kw
tier 1 elec = 10.31/.11877 = 87 hours to save $1
tier 2 elec = 10.31/.13502 = 76
tier 3 elec = 10.31/.27572 = 37
tier 4 elec = 10.31/.40577 = 26
tier 5 elec = 10.31/.47393 = 22
* On the 120 watt CFL reflector box, it says 23 watts, so it's really putting out less light. Both reflector, and 9 watt decorator, use normal CFL bulbs in a different glass package.
** 9 watt are decorator bulbs found in bathrooms.
*** Savings always apply to your highest rate, not the average.
**** w/h means watts per hour.
http://www.pge.com/tariffs/electric.shtml#RESELEC
There are "dimmable" bulbs, but I've only seen them a couple times. I have put normal CFL bulbs behind a dimmer, and they seemed to last okay, but I was pretty careful not to use the dimmer, so I cannot guarantee that it's okay. I've seen CFL bulbs for $1 at Grocery Outlet and Costco, and I presume that Target, Kmart, etc have them as well, at least sometimes.