Paul Wheaton has an interesting article and several videos on his website that expands on the Mythbusters experiment. He measures the average time it takes to do several common activities for which you'd typically need a light then measures the life span and energy usage of various types of bulbs under those conditions.
- CFLs cost more to manufacture and replace than they are worth in energy savings
- Only turning a light on when you need it is still the best way to save money on lighting costs
- Lighting is such a small percentage of the average electricity bill that you'd save a lot more electricity by buying a clothes line or replacing a water heater than by worrying about which type of light bulb to use.
I'm inclined to agree with the majority of his conclusions but different usage patterns will have different results. I live in Florida where the primary electrical use is cooling during the summer months. Most of my lights have CFLs in them because they give off less heat (though I usually only use ambient sunlight during the day). Paul lives in Montana and considers the heat given off by incandescent bulbs a bonus during the long winters.
Until I read his article I can honestly say I didn't realize that CFLs were subsidized. (What isn't these days?) If something requires large subsidies to hide its true cost it's hard to call it sustainable.
The IEEE has an article on bulb lifespans but doesn't give any concrete results. They do point to a worksheet published by the Lighting Research Center at Rensselaer Polytechnic Institute which you can use to do your own analysis. It includes a lamp life multiplier table for fluorescent lamps. Here is the table:
Average hours of lamp Lamp life multiplier
operation per start for fluorescent lamps
For some compact fluorescent
lamps with "soft start" electronic
ballasts, the values may be higher
than those shown in the chart.
This table by itself does not give a clear picture but it is obvious as you cycle a fluorescent lamp more frequently it's expected life span drops drastically. For lights that you use infrequently and for only short amounts of time (a closet light for instance) the cost of replacing a prematurely failing CFL can vastly outweigh the savings gained from its use compared to an incandescent bulb, which is affected far less by cycling.
Here is an excerpt from research published by this same institute back in 1998: