Households in the U. S. contain a total of 523 million
lights that are on 1 or more hours a day--282 million of these
are on 4 or more hours a day. The majority of these lights are
incandescent--88 percent of those on 1 to 4 hours and 85 percent
of those on 4 or more hours. Given the greater efficiency of compact
fluorescent lights, how much would households save if they replaced
their incandescent lights with compact fluorescents? Replacing
incandescent lights that are on for a short period of time with
compact fluorescents is not very cost effective, because compact
fluorescents cost so much more than incandescents (about 22 dollars
compared to 75 cents). However, at longer periods of use, compact
fluorescents do become cost effective, in spite of their high
initial cost. Figures 3.1 through 3.3 compare the total cost of
an incandescent light with a compact fluorescent light, using
the assumptions listed in Table 3.1.
Table 3.1 Assumptions
Used in the Comparison Between Compact Fluorescent
and Incandescent Lights
| Initial Cost of Bulb | 75 cents | 22 dollars |
| Wattage | 75 watts | 26 watts |
| Life of Bulb (hours) | 750 hours | 10,000 hours |
| Hours Used per Day | 6.7 hours | 6.7 hours |
Sources: Energy Information Administration,
Office of Energy Markets and End Use; Lighting Research
Center, Rensselaer Polytechnic Institute, The Lighting Pattern
Book for Homes, 1993.
Assumptions Used in the Calculation of Potential
Savings
Cost and Life of Bulb
A 75-watt incandescent bulb costs about 75 cents
and has a rated life of 750 hours. A 26-watt compact fluorescent
bulb costs about 22 dollars and has a rated life of 10,000 hours.
The calculations in this report assume there are no additional
costs involved in the replacement of incandescent lights, such
as bulb breakage or the purchase of new fixtures. They also assume
the bulbs last their rated number of hours, although the actual
life of light bulbs varies from bulb to bulb.
Light Output
Light output is measured in lumens. A 75-watt incandescent
bulb emits approximately 1,190 to 1,220 lumens while a 26-watt
compact fluorescent bulb emits about 1,550 lumens. Although an
18-watt compact fluorescent has the same light output rating as
a 75-watt incandescent (1,100 to 1,250 lumens), a bulb's rated
light output is not the only consideration in choosing a replacement
bulb. The location and position of the fixture affect the actual
output of compact fluorescent bulbs, and the quality of the light
may differ between compact fluorescents and incandescents. Consequently,
for satisfactory light output, a compact fluorescent bulb may
need a higher rated light output than the incandescent it is replacing.
For these reasons, a 26-watt compact fluorescent bulb is used
in the calculations, rather than an 18 watt bulb.
Hours of Use
Repeatedly switching a compact fluorescent light
on and off reduces the life of the bulb. Therefore, compact fluorescent
lights provide the biggest savings when they are used to replace
incandescent lights that are used several hours per day. The calculations
in this report are based on lights that are used four or more
hours per day. According to the Lighting Supplement data, these
lights are on an average of 6.7 hours per day.
Simple Payback
The calculations are based on 1993 dollars. They
do not take into account changes in energy costs or changes in
the value of the dollar over the lifespan of a compact fluorescent
bulb.
Universal Replacement
This report assumes that all incandescent lights
used four or more hours per day can easily be replaced by compact
fluorescent lights. This assumption ignores the fact that some
compact fluorescent bulbs may not fit into fixtures designed for
incandescent bulbs. The EIA does not have data on the percent
of fixtures that could be successfully converted to compact fluorescent
lights, so it is unclear how erroneous this assumption is.
Calculation of Savings
At a rate of use of 6.7 hours per day, a compact fluorescent bulb lasts, on average, about 4.1 years. By contrast, an incandescent bulb lasts about 3.5 months. Figures 3.1 through 3.3 show the savings that accrue over the expected life span of a compact fluorescent bulb. The figures include the cost of repeatedly replacing the incandescent bulb. The cost comparisons are calculated for three different electric rates--5, 10, and 15 cents per kWh.
When electricity costs 5 cents per kWh, compact fluorescent
bulbs save money after about 2.5 years and result in a total savings
of approximately 12 dollars by the end of the life span of the
compact fluorescent bulb (Figure 3.1). At a cost of 10 cents per
kWh, compact fluorescents save money after 1.5 years and result
in a total savings of 36 dollars (Figure 3.2). With the highest
priced electricity--15 cents per kWh, compact fluorescents save
money after only 1.1 years and result in a total savings of 60
dollars per bulb (Figure 3.3). The average household has only
2.5 incandescent lights that are on 4 hours or more, so assuming
the same amount of savings per light, their total savings due
to replacement would be twice the savings listed above. Therefore,
even at the most expensive electric rates, an average household
would save only about 120 dollars over a period of 4 years. For
many households, this may not be incentive enough for them to
purchase compact fluorescent bulbs.
Although these comparisons do not show a tremendous
dollar savings in using compact fluorescent lights, they do show
a sizable savings in electricity. In each of these three figures,
the line plotting the cost of the incandescent bulb has a steeper
slope than the line plotting the cost of the compact fluorescent,
especially at higher electric rates. What this shows is that with
incandescent bulbs, the life-cycle cost is composed largely of
electricity costs. On the other hand, the life-cycle cost of compact
fluorescent bulbs is made up mostly of the cost of the bulb itself.
For example, over a period of 4.1 years, at 5 cents per kWh, the price of electricity accounts for 37 percent of the life-cycle cost of a compact fluorescent light, but for 78 percent of the life-cycle cost of an incandescent light. Table 3.2 shows the cost of electricity and the cost of bulbs for fluorescent and incandescent lights, over a period of 4.1 years, by the price of electricity. The cost of powering a compact fluorescent bulb at the highest electric rate is little more than the cost of powering an incandescent at the lowest electric rate.
Another advantage of compact fluorescent bulbs is
convenience. Incandescent bulbs need to be replaced about 13 times
more frequently than compact fluorescent bulbs. In areas such
as hallways, where bulbs are hard to reach, and light quality
is not of utmost importance, the convenience of compact fluorescent
bulbs is a particular advantage.
(dollars) | (dollars) | (dollars) | (dollars) | |
| 5 | 22 | 12.68 | 10.5a | 36.56 |
| 10 | 22 | 25.35 | 10.5 | 73.13 |
| 15 | 22 | 38.03 | 10.5 | 109.69 |
a Over
a period of 4.1 years, a 75-watt incandescent bulb would have
to be replaced 13 times. The initial cost of the first bulb, plus
13
replacement bulbs, times the cost of each bulb equals $10.5 (i.e.,
14 bulbs at 75 cents each).
Source: Energy Information Administration, Office of Energy Markets
and End Use.
Potential aggregate U.S. household energy savings
for replacement of all incandescent bulbs used more than 4 hours
per day amounts to 31.7 billion kWh annually. [15]
This assumes that the average incandescent bulb is 75 watts and
is replaced by a 26-watt compact fluorescent bulb. Thirty-eight
percent of this savings, or 12 billion kWh, would come from replacing
the 44.1 million bulbs used 12 or more hours per day and 62 percent,
or 19.7 billion kWh, would come from replacing the 196.6 million
lights used 4 to 12 hours per day. These potential energy savings
are 35 percent of the electricity used for lighting in 1993 (91
billion kWh).
Two programs designed to encourage households to use compact fluorescent lights found that most of the participating households would not be willing to pay more than 10 dollars for a compact fluorescent bulb. [16] Given compact fluorescent bulbs cost 20 dollars or more, individual households may need some incentive to use them and to contribute to the aggregate savings in electricity.