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Light bulb FAQs

By Matthew Knight

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Light bulb FAQs

Find out the answers to the most commonly asked light bulb questions.

Buying new light bulbs is no longer as simple as popping into a shop and picking up a 60W replacement bulb. Here our experts answer the questions we're asked most frequently about light bulbs, to help you replace your old bulbs with energy-efficient equivalents.

What's happened to traditional light bulbs?

Old-fashioned incandescent bulbs have been phased out across Europe.

But not all energy-saving light bulbs are the same. Our tests have uncovered light bulbs that will save you money on your energy bills, last a long time, and match the colour and brightness on the packaging. We've also found bulbs that are inefficient, fail before they should and vary significantly from the claims on their packaging. 

Find out which energy-saving light bulbs are worth buying - head straight to our Best Buy light bulbs

What are the different types of light bulbs I can buy?

There are three types of energy-saving light bulb:

  • compact fluorescent lamps (CFLs)
  • halogens 
  • light-emitting diodes (LEDs).

For more details about which you should buy, visit our guide to how to buy the best light bulb.

Will using energy-saving light bulbs save me money?

Replacing just one 60W incandescent with a CFL bulb (the most common style of energy-saving light bulb) can reduce your electricity bill by around £7 a year, so replacing 10 light bulbs with energy-savers could save you £70 a year. LED bulbs are even more efficient than CFLs and save almost £7.50 per bulb per year. 

LEDs usually cost more to buy initially but have incredibly long life expectancies, so you may not need to replace them for up to 30 years. Halogen bulbs are the least efficient, so you’re unlikely to notice any reduction in your energy bill.

Which light bulbs are most similar to an old-fashioned 60W incandescent?

A 60W incandescent typically emits 700-900 lumens, so you’ll need to look for one with a similar brightness. Our five tips for choosing the right light bulb guide explains how the lumen and wattage values compare for each type of energy-saving light bulb.

In addition to the brightness, incandescent light has a ‘warm’ yellowish glow, so if you want to match this you’ll also need to consider the colour temperature. This is given in units called Kelvin (K) and should be listed on the packet. Incandescent light has a colour temperature of around 2,700K, so a similar value should give a similar coloured light, which is sometimes labelled as ‘warm white’ on the box.

Why are some energy-saving light bulbs more expensive than they used to be?

Until 2010, energy companies subsidised and even gave away CFL-type light bulbs to UK homes. But following concerns that consumers were not using the bulbs given to them, these direct promotions were banned and that has meant that the price of CFL bulbs has increased in the past few years.

Which wattage of light bulb should I replace my traditional light bulb with?

Read our five tips for choosing the right light bulb find out what wattage and lumens translate into for each type of light bulb.

Are all energy-saving bulbs slow to get bright when you switch them on?

LEDs and halogens come on instantly, but some CFLs still take a few minutes to reach full brightness. At Which? we check the light output of the bulbs we rate when they are first turned on, and also at intervals to ensure the measured light output meets what’s promised on the packaging. 

The results of our independent testing show which bulbs give out a good level of light when they're turned on and those that don't.

Go to our light bulb reviews to find the best and worst.

Can I use energy-saving bulbs in cold rooms or outside?

Colder temperatures are only a problem for CFLs, as LEDs and halogens should work well at all temperatures. We test the performance of CFLs at both 5ºC and -10ºC, and have found that some CFLs don't work well at low temperatures, making them less suitable for unheated rooms or outdoor spaces, such as a garage.

Can I use energy-saving bulbs with dimmers?

A bulb's suitability for use with dimmers should be written on the packaging, so check the box to find out whether the bulb is dimmable before you buy.

However, some dimmer switches may not be compatible with newer types of bulbs. In general:

  • CFLs and halogen bulbs - most modern dimmer switches should work with these bulbs, although some older ones may not be compatible
  • LEDs - you may need to upgrade your dimmer switch to cope with low electrical loads. If in doubt, ask an electrician to check.

Can I find bulbs for chandelier-style light fittings?

Manufacturers now produce energy-saving light bulbs in many more shapes and sizes than they used to - for example, candle and smaller globe-shaped bulbs.

If a light bulb fails, can I get a refund?

Warranties on LED bulbs typically last between two and four years, so if the bulb fails within this time you should be able to get your money back. Check the box for details, and contact the place of purchase or the manufacturer’s customer service department. 

You can also see more information on how to deal with faulty goods, including template letters, on our consumer rights website

Since I started using LED lights, my digital radio is playing up. Can LED bulbs affect digital radios?

Yes, we have found that some (but not all) LED bulbs can affect digital radios. Our snapshot tests found that some LEDs caused a fuzzy reception and even a complete loss of signal when placed within a few centimetres of the radio. We’re planning to test this further to find out exactly which bulbs are affected, and will let you know.

Which? was first alerted to this problem when a member told us his radio had stopped working after replacing all his kitchen lights with generic LED bulbs. We need your help to find out more: if you have experienced interference with your radio, let us know the bulb type and brand. We also want to hear from you if you know why this is happening. Find out how to contact us here.

How can I dispose of used energy-saving light bulbs? 

LEDs and halogens can be disposed of in your normal household waste, but CFLs need to be recycled because they contain tiny amounts of mercury.

You can find your nearest local recycling site by entering your postcode on the Recolight website. Homebase, Ikea, Robert Dyas and some branches of Sainsbury's often have recycling points.

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