Environmental Engineering Reference
In-Depth Information
an average U.S. household now leaks constantly about
50 W, or about 4%, of all residential electricity, mostly
owing to remote-ready TVs, VCRs, audio equipment,
and communication devices (Meier and Huber 1997;
Thorne and Suozzo 1997). Fortunately, these standby
losses can be cut to less than 1 W per device.
That lighting takes such a small share of the U.S.
household electricity demand is due not only to great
disparities in typical power ratings of lights and common
appliances (standard incandescent light bulb 100 W,
standard fluorescent tube 40 W, and compact fluorescent
23 W, compared to 1 kW for a small toaster) but also to
increasing efficacy (the quotient of the total luminous
flux emitted by the rated power, measured in lm/W) of
light (Smil 2003). In 1882 carbonized fibers in Edison's
first lamps produced a mere 1.4 lm/W, and by 1900
their performance improved to 3-3.55 lm/W. Osmium,
introduced in 1898, delivered 4 lm/W, tungsten fila-
ments in vacuum 10 lm/W and in inert gas-filled bulbs
(in 1912) 12 lm/W. Today's standard incandescent
lights rate about 15 lm/W, which means (using 1.47
mW/lm as the standard mechanical equivalent of light)
that they convert about 2.2% of electricity into light (fig.
9.10). New techniques boosted this performance. Fluo-
rescent lights go as high as 100 lm/W (15% efficiency),
and the best performers are low-pressure sodium lamps
used for outdoor illumination (up to 175 lm/W, or
nearly 26%). The next wave will see spreading indoor
applications of light-emitting diodes (LEDs), which are
already widely useed in brake lights and flashlights. By
2006 the best efficacy of white-light LEDs surpassed
100 lm/W.
Before post-WW II affluence spread the residential
use of electricity beyond basic lighting and simple refrig-
eration to space heating, air conditioning, freezing, wash-
9.10
Increasing efficacy (lm/W) of electric lighting, 1920-
2000. From Smil (2003).
ing, and scores of other uses served by a still-growing
assortment of electronic devices, electricity's ascent first
revolutionized industrial production when it became the
dominant source of motive power. As revolutionary as
was the substitution of waterwheels by steam engines in
nineteenth-century factories, that step did not change
the mode of distributing the mechanical energy needed
for countless processing, machining, and assembling
tasks. Factory ceilings were clogged by complex arrange-
ments of iron or steel line shafts connected by pulleys
and belts to parallel countershafts, which were belted to
individual machines. Disabled, the prime mover (water-
wheel, steam engine), a cracked line shaft, or a slipped
belt shut down the whole assembly; conversely, if most
of the machines did not need to work, the whole system
still kept on running.
Electric motors changed this rapidly, first driving rela-
tively short shafts for groups of machines and since the
