Light bulbs are measured in watts, which is how much energy they use.  A typical light fixture in your home takes a 60 watt bulb, but if it were a CFL, which is more energy efficient, you would only need 13 watts to give you the same amount of light.  This can be confusing when you just want to replace that burned out light and can’t find the same wattage on the shelves at your hardware store. 

Light bulbs can also be measured in lumens, which is the amount of light they give off, or brightness.  In the example below, the incandescent bulb gives off 820 lumens of light and uses 60 watts, whereas the CFL (on the right) gives off 870 lumens of light and uses only 13 watts.

Compact fluorescent bulbs can produce the same amount of light (lumens) as a traditional incandescent bulb, while using significantly less energy (watts).  However, current light bulb packaging only advertises watts, but in mid-2011, the packaging will be more like nutrition facts that call out lumens, the estimated yearly energy cost, lifetime expectancy and light temperature of the bulb.

Late one night, many years ago, I was flying into Chicago and my seat mate was an executive in the “Bulb Division” of General Electric.  He said “yeah, I know it’s not the most glamorous product, but look out there,” and he gestured to millions of Chicago’s  twinkling lights below us as we approached O’Hare, “Every one of those bulbs is going to burn out.”  And I understood why GE, a manufacturer of locomotives, jet engines, and MRI scanners (to name just a few), was still in the seemingly humble light bulb business – and why they remain so to this day.

Incandescent light bulbs are not profitable because they are priced so high (although a cartel did artificially inflate bulb prices in the 1920s and 30s).  Incandescents are profitable for two reasons: 

1. Their design hasn’t changed in 100 years, so they are cheap to manufacture.
2. Like my seat mate said:  they burn out quickly, after only around 1,000 hours of use.  Manufacturers get to sell you these “cheap” bulbs over and over again. 

While manufacturers are very happy when you buy incandescent bulbs, what about your end of the deal?  The price tag on incandescents is up to ten times cheaper than compact fluorescents (as low as 20 cents per bulb versus about 2 dollars), but because they burn out ten times more frequently (1,000 hours versus 10,000 hours), bulb costs for the two types are actually identical over time. 

The real kicker is that because incandescents are so inefficient (they use 90% of the energy they consume to create heat, not light), it costs about 5 times as much for the electricity to run them versus compact fluorescents.  How much money are we talking here?  Over 10 years, those seemingly cheap 20 cent bulbs are going to be costing you thousands of dollars in wasted electricity.

Something to keep in mind next time you see that “incredible sale” on incandescent bulbs at the hardware store.