has an average power consumption of 42 000W. So having the lights on
while driving requires 2% extra power.
What about the future’s electric cars? The power consumption of a
typical electric car is about 5000 W. So popping on an extra 100 W would
increase its consumption by 2%. Power consumption would be smaller
if we switched all car lights to light-emitting diodes, but if we pay any
more attention to this topic, we will be coming down with a severe case of
every-little-helps-ism.
Generally I avoid discussing economics, but I’d like to make an exception
for lightbulbs. Osram’s 20 W low-energy bulb claims the same light
output as a 100 W incandescent bulb. Moreover, its lifetime is said to be
15 000 hours (or “12 years,” at 3 hours per day). In contrast a typical in-
candescent bulb might last 1000 hours. So during a 12-year period, you
have this choice (figure 9.3): buy 15 incandescent bulbs and 1500 kWh of
electricity (which costs roughly £150); or buy one low-energy bulb and
300 kWh of electricity (which costs roughly £30).
It feels like a waste, doesn’t it? Someone put resources into making the
old incandescent lightbulb; shouldn’t we cash in that original investment
by using the bulb until it’s worn out? But the economic answer is clear:
continuing to use an old lightbulb is throwing good money after bad. If you
can find a satisfactory low-energy replacement, replace the old bulb now.
Researchers say that LED (light-emitting diode) bulbs will soon be even
more energy-efficient than compact fluorescent lights. The efficiency of a
light is measured in lumens per watt. I checked the numbers on my latest
purchases: the Philips Genie 11 W compact fluorescent bulb (figure 9.4)
has a brightness of 600 lumens, which is an efficiency of 55 lumens per
watt; regular incandescent bulbs deliver 10 lumens per watt; the Omicron
1.3 W lamp, which has 20 white LEDs hiding inside it, has a brightness
of 46 lumens, which is an efficiency of 35 lumens per watt. So this LED
bulb is almost as efficient as the fluorescent bulb. The LED industry still
has a little catching up to do. In its favour, the LED bulb has a life of
50 000 hours, eight times the life of the fluorescent bulb. As I write, I
see that www.cree.com is selling LEDs with a power of 100 lumens per
watt. It’s projected that in the future, white LEDs will have an efficiency
of over 150 lumens per watt [ynjzej]. I expect that within another couple
of years, the best advice, from the point of view of both energy efficiency
and avoiding mercury pollution, will be to use LED bulbs.