Bulbs: *All dimmable so it's apples to apples* (Prices from Home Depot website as of 12/11/2012 1:30 pm DST)
Philips 12.5w LED - $12.97 - 800 lumens / Life: 25,000 hours
EcoSmart 14w CFL 2-pk - $5.97 - 850 lumens / Life: 10,000 hours
Philips 60w 16-pk - $3.97 - 860 lumens / Life: 1,000 hours
Raw cost to lifespan comparison: LED $12.97 = CFL $7.4625 = Incandescent $6.203125
Electric rate: *Rates will increase over time so actual ROI will be faster than shown in this math*
$10.4/Kwh
$17/Kwh
"Between 2005-2010, 49 out of 50 U.S. states experienced an increase in their average cost per watt for electricity. On average over the five years, retail electricity costs in the U.S. increased by 4.1 percent annually. In real dollars, the average cost/kWh increased by a total of 1.8¢ from 2005-2010."
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www.renewableenergyworld ··· -the-u-sUsage: *Average daily use*
4 hours/day 261 days/year (M-F) - 1,044 hours
4 hours/day 365 days/year - 1,460 hours
8 hours/day 365 days/year - 2,920 hours
LED:
1,044 hours
$10.4/Kwh = 1,044 * 12.5 = 13,050 / 1,000 = 13.05 * .104 = $1.3572
$17/Kwh = 1,044 * 12.5 = 13,050 / 1,000 = 13.05 * .17 = $2.2185
1,460 hours
$10.4/Kwh = 1,460 * 12.5 = 18,250 / 1,000 = 18.25 * .104 = $1.898
$17/Kwh = 1,460 * 12.5 = 18,250 / 1,000 = 18.25 * .17 = $3.1025
2,920 hours
$10.4/Kwh = 2,920 * 12.5 = 36,500 / 1,000 = 36.5 * .104 = $3.796
$17/Kwh = 2,920 * 12.5 = 36,500 / 1,000 = 36.5 * .17 = $6.205
CFL:
1,044 hours
$10.4/Kwh = 1,044 * 14 = 14,616 / 1,000 = 14.616 * .104 = $1.520064
$17/Kwh = 1,044 * 14 = 14,616 / 1,000 = 14.616 * .17 = $2.48472
1,460 hours
$10.4/Kwh = 1,460 * 14 = 20,440 / 1,000 = 20.44 * .104 = $2.12576
$17/Kwh = 1,460 * 14 = 20,440 / 1,000 = 20.44 * .17 = $3.4748
2,920 hours
$10.4/Kwh = 2,920 * 14 = 40,880 / 1,000 = 40.88 * .104 = $4.25152
$17/Kwh = 2,920 * 14 = 40,880 / 1,000 = 40.88 * .17 = $6.9496
Incandescent:
1,044 hours
$10.4/Kwh = 1,044 * 60 = 62,640 / 1,000 = 62.64 * .104 = $6.51456
$17/Kwh = 1,044 * 60 = 62,640 / 1,000 = 62.64 * .17 = $10.6488
1,460 hours
$10.4/Kwh = 1,460 * 60 = 87,600 / 1,000 = 87.6 * .104 = $9.1104
$17/Kwh = 1,460 * 60 = 87,600 / 1,000 = 87.6 * .17 = $14.892
2,920 hours
$10.4/Kwh = 2,920 * 60 = 175,200 / 1,000 = 175.2 * .104 = $18.2208
$17/Kwh = 2,920 * 60 = 175,200 / 1,000 = 175.2 * .17 = $29.784
Power: CFL $6.9496 - LED $6.205 = $0.7446 ($17/Kwh)
Cost: LED $12.97 - CFL $7.4625 = $5.5075
$5.5075 / $0.7446 = ~7 years 5 months to break even / If you take a 20% Kwh increase into account it's ~6 years
Power: CFL $4.25152 - LED $3.796 = $0.45552 ($10.4/Kwh)
Cost: LED $12.97 - CFL $7.4625 = $5.5075
$5.5075 / $0.45552 = ~12 years to break even / If you take a 20% Kwh increase into account it's ~9 years 7 months
As you can see how much you use a light and your power price play a large role in figuring out what's cheapest over a given period of time. If you factor in a 4.1% annual Kwh increase that reduced the ROI by about 20-25%. Anyone can see incandescent are just a money pit while CFL and LED fight for most cost effective spot based on usage/Kwh rate. If the light is hard to access like a 10+ foot ceiling you need to add more cost onto the CFL to account for the man hours to pay someone to replace them 2.5 times more often. Lots of other factors play into it but this is just a basic rundown to get people started.