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.

The economics of low-energy bulbs

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).

Should I wait until the old bulb dies before replacing it?

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.

What about the mercury in compact fluorescent lights? Are LED
bulbs better than fluorescents?

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.

Figure 9.3. Total cumulative cost of using a traditional incandescent 100 W bulb for 3 hours per day, compared with replacing it now with an Osram Dulux Longlife Energy Saver (pictured). Assumptions: electricity costs 10p per kWh; replacement traditional bulbs cost 45p each; energy-saving bulbs cost £9. (I know you can find them cheaper than this, but this graph shows that even at £9, they’re much more economical.)

Figure 9.4. Philips 11 W alongside Omicron 1.3 W LED bulb.