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...

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