Owens Corning
Energy Saver Worksheet: Compact Fluorescent Lights
How can spending almost $30 to buy a single light bulb possibly save you money? Spend a few minutes filling in this worksheet and you'll be surprised. The compact fluorescent light (CF) uses only about 20 watts of energy to produce the light of a standard 75 watt light bulb and lasts about 10 times as long. The more you pay for electricity, the larger your savings. If you can purchase the compact fluorescent light on sale (less than the $29 assumed on the worksheet), enter that figure and it will increase your savings dramatically.

First, calculate the cost of a kilowatt-hour of electricity by dividing your total electric bill by the total KWH used for that period. If your bill was, let's say, $51.28 last month and you used 587 KWH, then the cost per KWH is 51/587 or .087.

We figured a standard bulb costs about a dollar, but if you know the price you actually paid, use it to calculate the cost of 10 light bulbs you'll have to buy to equal the life of a compact fluorescent light. Figure the cost of operating the standard 75-watt bulbs by multiplying the watts used times 9000 hrs (the life expectancy for the compact fluorescent) times your cost of energy to get $59. Add this figure to the cost of 10 bulbs and you get $69, the total cost of operating a standard light for 9000 hrs.

The cost of operating a compact fluorescent is figured in the same way. The light uses 20 watts for 9000 hrs at .087 a KWH for a cost of $15.66 Add to this the $29 (use the actual cost if you know it) and you find that it cost only $44.66 to run the light. The savings is $24.34 for each light. If you plan to replace 5 lights, then you can expect to save about $121.70 over the life of the compact fluorescent.

Estimate Savings by replacing a 75 watt bulb with a Compact Fluorescent

Cost of KWH (1) $ ____________ (from line (4) Cost of Energy)

Cost of 75 watt bulb (2) $ ____________

Cost of Compact Fluorescent (3) $ ____________

Operating cost of a 75-watt bulb:

((75w X 9,000hr)/1000w) X Cost of KWH

675 X (1) $ _________ = (4) $ ____________

Replacement cost:

10 bulbs X (2) $ __________ = (5) $ ____________


Total (4) + (5) (6) $ ____________

Operating cost 20 watt Compact Fluorescent:

((20w X 9000hr)/1000w) X Cost of KWH

180 X (1) $ _________ = (7) $ ____________

Replacement cost:

1 bulb X (3) $ __________ = (8) $ ____________


Total (7)+(8) (9) $ ____________

Savings per Bulb

(6)-(9) (10) $ ____________

Number of replacements (11) ____________

Total Saving (10) X (11) (12) $ ____________

The savings here is the difference between the electricity used by a standard bulb (SB) minus the electricity consumed by the fluorescent light. With an electric bill, the reader can calculate the cost per kilowatt hour and then figure the savings. The longer life of the compact fluorescent (CF) bulb must also be factored in. You would have to replace the standard bulb 10 times or more since it has a much shorter life span.

SAMPLE CALCULATIONS

Cost of energy:

$51.28 / 587 KWH .087 KWH

Cost of replacing 10 SB @ $1.00: $10.00

Cost of operating 75 watt light

(75 X 9000)/1000) X .087 $59.00

Total: $69.00

Cost of replacing with CF @ $29.00: $29.00

Cost of operating CF bulb (20 watts)

((20 X 9000)/1000) X .087 $15.66


Total $44.66

Unit Saving $24.34

Number of lights you use over 4 hours: 5

Total Savings

5 * 24.34 $121.70

Assumptions:

9000 hrs is average life of (CF) compact fluorescent bulb

Formulas:

Cost of KWH = Bill total / Monthly KWH

Operating Cost = (watts X 9,000 hrs)/1000)=KWH) X .087

Total = Replacement cost + Operating cost

Unit Saving = Total cost old - Total cost new

Total Savings = Unit Savings X Number replaced

Written by the editors of HouseNet
Copyright HouseNet, Inc.

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