How do light switch dimmers work Do they just reduce the voltage

A. Originally, yes. Light dimming technology has been around for some time, although to start with it was used mainly in theatres. Originally devices that reduced the amount of voltage getting to the light - by sending it through a coiled, and therefore longer, circuit - were large, expensive and not very efficient.

Q. So, how does the dimmer switch on my kitchen light work

A. These small and inexpensive devices use something called triacs. Triacs work by chopping up the voltage, making the light appear dimmer than if it received the full voltage.

Q. Why doesn't the light just flicker on and off

A. Because the interruptions happen many times a second - too fast for us to see them - so that we see a constant dimmed light, rather than one that flicks on and off.

Q. Why does the bulb buzz when the light is dimmed

A. Although we don't see the increase and decrease in voltage that the bulb receives, the filament certainly senses it. The buzzing is the sound of the filament vibrating in response to the sudden changes in the flow of current.

Q. Can I do anything about it

A. Buzzing bulbs are often the sign of a cheap dimmer switch. A good dimmer should contain a filter which smoothes out the chopped up current. But some cheaper dimmers cut costs by reducing the amount of filtering. So, you could try fitting a more expensive and hopefully better made dimmer switch.

Alternatively try replacing the bulb, some cheaper brands have rather flimsy supports for their filaments. A sturdier support may stop the filament from vibrating and therefore buzzing.

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by Lisa Cardy