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Frequently Asked Questions on Dimmable Light Bulbs

What are dimmable light bulbs?

Dimmable bulbs are specifically manufactured for dimmable fittings (i.e. when you have a dimmer switch on the wall). They’re popular due to their aesthetic and energy-saving potential: the ability to lower the lighting can completely change a room’s ambience while using less energy. Most modern light bulbs, such as LEDs and halogen, are available in dimmable versions but fluorescent tubes need to be fitted with a dimmable ballast.

Why do I need to install a dimmable ballast to dim fluorescent tubes?

Just like any dimmable bulb, fluorescent tubes need to have the right control gear in it to be dimmable. Without a dimmable ballast, fluorescent tubes can’t be dimmed.

What are the best dimmable light bulbs?

This will depend on what type of fitting you have but if it’s for downlight LEDs then the All In One LED dimmable downlight 10w (known as the SOLO) is an ideal choice as the colour temperature can be adjusted from warm white, cool light to daylight and comes with a number of different fascias.   For a cheaper option for a downlight try one of the 8w downlight range, these bulbs have weatherproof fascias, are dimmable and are fire-rated to comply with building regulations.

Are dimmable light bulbs available for outdoor use?

Yes, dimmable outside lights are possible but need to be fitted with a dimmer switch, ideally this should be a trailing edge dimmer for use with LEDs or a basic leading edge dimmer for halogen lights or similar. Fluorescent bulbs also need the right control gear to enable them to be dimmed, whether it’s fitted indoors or out. Any outdoor light fittings will need to be IP rated so they aren’t affected by water.

If you are wanting to dim an outdoor light such, as a downlight in a garage soffit for example, you need IP65 rated downlight fittings and an appropriate dimmer switch, ideally controlled within the house.

Although available, bulbs with dimming capabilities aren’t commonly fitted outdoors as most people want the maximum amount of light in a garden, rather than a dim light.

You can find out more about lighting for outdoors with our Ultimate Guide to Outdoor Lighting for Your Garden, which includes more information on IP ratings.

Can CFLs be dimmable?

Yes, but you should only use a dimmable CFL in a dimmable fixture. If you try to fit a dimmable CFL in a non-dimmable fitting then the bulb is likely to flicker.

How can I tell if a light bulb is dimmable?

Check the packet to see if a bulb is dimmable. It will have one of the following symbols on it:


Do dimmable lights need special bulbs?

Yes, only bulbs marked ‘dimmable’ on the packaging will be compatible with a dimmable fitting.

Can I fit a non-dimmable bulb into a dimmable fitting?

No, it’s not recommended to put a non-dimmable lamp into a dimmable fitting. Any sort of adjustment on the dimmer, even if by accident, could cause melting from heat and blowing of the lamp. To avoid this, just stick to dimmable lamps only or have the dimmer removed from the circuit, or buy a compatible dimmable bulb instead if you do want dimming capabilities.

Can I fit dimmable lights in a bathroom?

Yes, dimmable lights can be used in bathrooms and can be operated with dimmable pull cords. Dimmable pull cords work by pulling the cord for a prolonged length of time until you find the right light level for your bathroom. Regular dimmer switches are not recommended for use in bathrooms as they are deemed unsafe due to the proximity of water and won’t be approved by building regulations. An alternative to installing a dimmable pull cord is to fit a standard dimmer switch outside the bathroom.

Are dimmable light bulbs available for under cabinet lighting?

Dimmable under cabinet lighting can add a versatile addition to the lighting set up in your kitchen. LED tubes and downlights are an excellent choice for under cabinet lighting. LEDs, fluorescent tubes and halogen bulbs are all dimmable and all suitable for under cabinet lighting, depending on the fitting you have.

Are dimmable light bulbs available for recessed lighting?

Yes, dimmable LEDs are a good choice for recessed lighting. When choosing your LEDs (or any other type of bulb), ensure that the bulb is dimmable. If you are upgrading from halogen bulbs to LEDs then you might need to replace the existing recessed light with a dedicated LED housing and trim instead of just replacing the bulb.

A great option for this are the 8w LED downlights as they have weatherproof fascias, are fire-rated to comply with building regulations and are dimmable. For commercial purposes, the 40w LED panels are also dimmable.

Why is my dimmable light bulb buzzing?

When a light bulb is dimmed, it isn’t because there is less power going to the bulb, it’s actually because the bulb is switched on and off so quickly that it looks as though it’s generating less light. In some cases, the rapid switching on and off can create a buzzing sound.

The most likely reason for a buzzing bulb is that the light bulb used in the fitting is not a dimmable bulb. Your first check should be to change the bulb for a dimmable one and see if this stops the buzzing. If changing the bulb doesn’t work then try changing the dimmer switch to a more modern version. Cheap or old dimmer switches don’t dampen the vibration from the electromagnetic field within the dimmer switch, and this can cause the buzzing effect.

Why is my dimmable light bulb flickering?

As with buzzing bulbs, the most common reason why a dimmable bulb flickers is that it is not compatible with the dimmer switch. The first option is to change the bulb, and then if this doesn’t make a difference, upgrade the dimmer switch.

How will I know if a bulb is the cause buzzing or flickering?

dimmable bulb caution

Whether a bulb is dimmable or not will be clearly marked on the packet; however, there may also be the following symbol as well, which indicates that the bulb may not be suitable for use on certain dimming systems. With LEDs, this symbol indicates that the bulb will work better with a trailing edge dimmer rather than the old fashion leading edge dimmers.

How do dimmable LED light bulbs work?

Unlike other types of dimmable bulb, LEDs are not dimmed by a drop in voltage. The LED creates a dimming effect through either pulse width modulation (PWM) or analogue dimming. PWM is a digital signal whereby the LED is either on or off and the lower you set the dimmer, the less the signal is on, and vice versa. The human eye then assimilates the average amount of light from this ‘pulsing’ effect.

With analogue dimming, the current being fed to the LEDs is reduced.

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Published 2012/11/16

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