240V LED Bulbs and Dimmer Switches

In the REUK Shop we sell a range of energy efficient lighting products. One of the top sellers is the 240 Volt AC GU10 LED Spotlight Bulb.

GU10 LED spotlight bulb - cannot be used with a dimmer switch

Providing the same amount of light as a 25 Watt halogen spotlight, but with a consumption of just 1 Watt of electricity and a lifetime of 50,000 to 100,000 hours, these bulbs are fantastic money-savers and are good for the environment. However, we have to sell them with the disclaimer that “these bulbscannot be used with dimmer switches“.

In this article we will look into why 240V LED bulbs cannot generally be used with dimmer switches.

How do Dimmer Switches Work

LED Bulb Dimmer Switch

Domestic dimmer switches work in one of two different ways.

The old way used a variable resistor to reduce the amount of voltage available for the bulb. As the user (wanting to dim the lights) turned the dial of the dimmer, the resistance increased. This caused some of the electricity supply to be lost as heat in the resistor leaving less available for the bulb (which therefore glowed less brightly).

Modern dimmer switches use electronics to increase efficiency and safety. The alternating current(AC) of mains electricity has a varying polarity moving from a positive voltage to a negative voltage 50-60 times per second. The modern dimmer switch simply turns off the power to the lighting circuit every time the electricity supply changes polarity – with the time spent in the off-state controlled by the dimmer switch.

When the lights are very dim, the power to the lighting circuit is kept off for a (relatively) long time, and when the lights are bright, the power to the lighting circuit is on almost all the time. The human eye cannot detect the lights strobing on and off more than 100 times per second and so the lights appear to just change in brightness.

For more detailed information on dimmer switches click here to read the article How Dimmer Switches Work from the excellent howstuffworks.com website.

Dimmer Switches and 240V AC LED Bulbs

In short, the old-fashioned style of dimmer switch CAN be used with LED bulbs. The internal variable resistor in the dimmer switch simply reduces the amount of voltage available for the bulb which in turn reduces its brightness.
Note that LED bulbs are far more sensitive to voltage than conventional incandescent and halogen bulbs, and so small changes made to the dimmer switch setting have a much larger effect on bulb brightness.

The new style of dimmer switch which turns the supply on and off CANNOT be used with 240V AC LED bulbs as it will seriously reduce their operational lifetime.

To find out what kind of dimmer switch you have it is not necessary to be an electricity-whizz. If the dimmer switch feels warm to the touch when the lights have been on and dimmed for a while, you have the old type, otherwise you have the modern version.

The Future

Hopefully, as mains powered LED bulbs become more common someone will come up with an affordable dimmer switch which works safely with LED bulbs, or do something to the electronics inside each LED bulb so that they can be used with existing modern dimmer switches.

Note that 12V DC LED bulbs CAN be used in 12V DC dimming circuits.