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Home & garden.

Updated: 30 Jun 2021

CFL light bulbs explained

Find out everything you need to know about classic energy-saving (CFL) light bulbs.
Haddi Browne
Lightbulbs 1

There are three types of energy-saving light bulb: compact fluorescent lamps CFLs (the most common type of light bulb), halogens and LEDs. Here, our experts tell you everything you need to know about CFLs.

What are CFL lights?

CFL (compact fluorescent lamp) light bulbs are the most common type of energy-saving bulb. They are the original energy-efficient alternative to now defunct traditional incandescent bulbs. CFLs typically use 60-80% less energy than an incandescent, halogens use 20-30% less and LEDs use an astonishing 90% less.

Discover which LEDs are the best – click to see Best Buy light bulbs.

Old-style incandescent bulbs had a filament inside that was heated until it glowed, which meant they used up energy to generate heat. 

CFL bulbs don't have a filament; instead they use an electric current to excite gases within the bulb that then cause a phosphorous coating on the inside of the bulb to glow, producing light. This method means less energy is lost to heat and the bulb uses less energy.

Until recently, CFLs were the most common type of energy-saving light bulb. They often come in stick and spiral shapes, although some are now disguised as traditionally shaped bulbs. You can buy CFL light bulbs from many high-street shops and they typically cost between £2 and £15.

What are CFL light bulbs great at?

CFLs are a good compromise between purchase price and energy saving. They are reasonably cheap to buy, with prices starting as low as £2. This means they will pay for themselves with energy savings pretty quickly when compared to traditional incandescent bulbs.

They have long lifetimes of about 10,000 hours (roughly about 10 years of use). This is not as long as LEDs, which claim to last up to 25,000 hours. But it is better than halogens, which last closer to 2,000 hours. 

To see which light bulbs last the longest in our tough tests, check out our light bulb reviews.

What are the downsides of CFL bulbs?

  • one of the main complaints about CFL bulbs is that they take a bit of time to warm up and get bright when they are first switched on. Newer CFLs are better at this, but it does mean that CFLs aren't always the best choice for lighting on stairs or bathrooms, where you want your light bright and instant. When we test light bulbs at the Which? test lab, we measure how long each takes to brighten to ensure we only recommend the quickest and brightest as .
  • CFLs contain a small amount of mercury, so they should be recycled and you need to be careful when handling them (especially if they break).
  • some CFLs aren't suitable for dimmer switches, so if you like being able to dim your lights then make sure you check the box before buying a CFL.
  • some CFLs can’t be used outside or work poorly in cold temperatures.
  • CFLs aren't always suitable for stairways or bathrooms, as some bulbs take a little time to warm up and reach full brightness.
  • some look quite different from old-style bulbs and it can be harder to get them in small shapes, such as candles.

Should I buy CFL bulbs?

CFLs are a good option and are the second most energy-efficient type of bulbs behind LEDs. Make sure you look at our independent reviews before buying, as there are some duds out there. The best examples of these bulbs offer a light that is close to your old incandescent, last for a decade and don't cost very much.

The worst won't last as long as our Best Buys, and won't match the claims on their packaging.

Pros: Warm, soft light close to traditional incandescent, affordable, long lifetime, more energy efficient than halogens

Cons: Can take time to brighten, difficult to dispose of, can look ugly when switched off