Energy and Power

Example. 2008 Olympic Performances

Event Time Speed
100 m 9.69 sec 37.2 km/hr
1500 m 3:26 min 26.2 km/hr
10000 m26:18 min 22.8 km/hr
marathon (42.19 km) 2.04 hr 20.4 km/hr

No hard data on energy consumption to achieve such performances. Studies do show ratio of anerobic to aerobic metabolism drops from 4 with length of event.

Compact Fluorescent Light Bulb vs Incandescent

(Blog Ref:, by ben 02/18/08)

DOE says: Lighting in US accounts for 22% of electricity comsumption and costs $58 B. If every home replaced just one bulb with compact fluoresecent light bulb (CFL), there would be both $600 M/yr savings in energy and 800,000-car reduction of greenhouse gas emission.

This simplistic analysis counts only saving to the consumer and not the other costs associated with CFL. The larger problem (as in final paper) is the total cost of energy -- and it will be borne by consumer one way or another.

Cradle to grave or dust-to-dust costs

Production and recycling. True costs must include not only consumer costs but production and recycling costs. The later are higher for CFL that contains more glass than incandecent, phosphor, 5 mg mercury, ballast (24-component chip).

Lifetime. Incandescent bulb puts ~90% of its energy into heat. In CFL current between filaments stimulates mercury to radiate UV radiation (and some heat); UV tranforms into mainly visible light through phospor coating on the tube. CFL put 25% of energy into light, rest into heat.

CFL vs Incandescent (kWh)
Component CFL Incandescent 8 Incandescent
Glass 0.17 0.11 0.88
Plastic 0.68 0 0
Electronics 0.66 0 0
Brass 0.18 0.18 1.44
Operation* 120 60 480
Recycle** 1.69 0 0
Total 123.4 60.3 482.3
*Assume CFL last 8000 hr & incandescent 1000 hr.
**Assumes energy to recycle CFL equals production.

Bulb for bulb CFL neads 5.7 more energy to make than incandescent but last 8 times long. Favors CFL.

In operation, CFL needs 120 kWh where as 8 incandescent need 480 kWh. Favors CFL.

Recycling favor incandescent.

Don't even have to trust CFL last 8 times longer. It turns out if you think about it, the breakeven point is about 69 hrs (ben got 50). Beyond that CFL is cheaper.

Incandescent: strong voltage dependence

The rating of incandescent light bulbs vary with manufacturer because of strong senstivity to supply voltage.

Property Voltage dependence
Lumens (light output) V3.4
Power consumption V1.6
Lifetime 1/V16

"Long-life" bulbs are achievd by reducing operating voltage: 5% reduction more than doubles lifetime with only 20% reduction of lumens.


Any table for light equivalency must be taken with grain of salt -- for example, this table from Energy Star.

Incandescent Equivalent CFL
Watts Lumens Watts
40 450 9-13
60 800 13-15
75 1100 18-25
100 1600 23-30
150 2600 30-52