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Q.We know that compact fluorescents deliver energy savings, but how about dimmer switches? The assumption is that homeowners will use them to turn down lights to save money — but do they actually save energy?

A.Sean Kenney, a master electrician in Amesbury, Mass., responds: Using a dimmer switch is an inefficient way to save energy. You’ve probably noticed that dimmer switches get warm when in use; while efficient electronic dimmers don’t get as hot as the old resistor-based models, they still heat up, which means that they’re consuming electricity.

To evaluate a lighting product’s energy efficiency, you need to consider not just wattage but also lumens, a measure of light output. Dimmed bulbs use more watts per lumen than undimmed bulbs and are therefore less efficient. So a 100-watt incandescent bulb dimmed to half brightness consumes more electricity than a 50-watt bulb operating at full output.

The best way to save electricity is to use the lowest-wattage bulb possible that will get the job done. In many circumstances, this means a compact fluorescent lamp (CFL), which draws roughly 14 watts to provide the same number of lumens as a 60-watt incandescent lamp.

CFLs aren’t without their drawbacks, however: They take a while to achieve full brightness, for instance, which can be a problem in areas where lights get turned on and off frequently, like stairways and hallways. Also, CFLs contain small amounts of mercury, which can complicate disposal. Some electricians argue that the energy used in the disposal process should be factored in when calculating a CFL’s total energy consumption.