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  • Compact Fluorescent Lamps (CFLs) save power consumption and carbon emissions compared to Filament lamp
  • Cost saved is normally many times their purchase cost (and this is with taking into account the value of the heating effect of filament lamps)
  • Energy saved is many times bulb manufacture energy
  • CFLs vary in light quality, a minority are poor
  • Power equivalents claimed on packaging tend to mislead
  • CFL lighting doesn't save a lot compared to other ways to save energy & money, but its a relatively easy option
  • Some people don't like the look of CFLs
  • Read also LED Lighting


GE made the first CFL in 1976, but its prohibitive cost prevented mass production.

Philips produced the first commercially successful CFL, the SL18 in 1980. Weight and size were a bit bigger than a can of beans, due to the 50Hz iron cored ballast. The weight made most tablelamps unstable.

Osram's electronic CFL in 1985 brought flash-free starting, much smaller size & weight and improved efficiency.

Lamps with separate ballast & tube such as PL-L, PL-C, 2D etc have become unpopular for domestic use. While a separate tube & ballast has one obvious advantage, the practical implementation of these has proven disadvantageous in terms of cost, convenience and flexibility.

Power Equivalence

Packet quoted power equivalents are misleading if compared to standard GLS filament bulbs. This continuance of misleading claims has put a good many people off using these light sources, as fitting a lower output lamp often makes a room look badly lit. The packet figures are actually comparisons to softone filament lamps, which produce less light than standard GLS filament lamps.

CFLs are at best 4x as energy efficient, so 1/4 the filament wattage is a good first approximation. (The ratio changes for lowest power lamps because 240v filament lamps fall off in efficacy at low powers more than CFLs do.)

Approx power equivalence:

  • 100w: 25w
  • 75w: 20w
  • 60w: 15w
  • 40w: 11w
  • 25w: 5w
  • 15w: 3w

Power equivalence in detail

Total lumen output comparison of filament and CFL lamps is not the whole story, for 3 reasons.

First the output of both fillament and CFLs reduces over time, but CFL output reduces a lot more than do filaments. Hence a 1000 lumen rated CFL isn't entirely equivalent to a 1000 lumen filament lamp.

Second, the light output distribution of the 2 is different, due to their differing light source shapes. Filament lamps give maximum light output at the top, with little variation with angle. CFL output varies with viewing angle by around 3:1, with maximum at the side, and minimum at the top.

Third, CFLs have a relatively bulky and somewhat light absorbing surface, so reflector type CFLs and CFLs fitted in an external reflector have reduced output. The initial tendency for CFLs to give most light in what is not the wanted direction with reflector lamps only worsens this.

  • Power equivalence is nearer 3:1 for reflector uses.
  • Miniature compact reflector lamps can see power equivalence nearer 2 or 2.5x, as much of the light emitted from the rear of the lamp is lost.

Sample Saving Calculation

To see if these lamps really save anything, we will compare a 100w filament bulb with a 25w CFL used in a centrally heated house.

We will use the following figures, which vary from case to case:

  • Light use: 5.5hrs/day average = 2000 hrs/year
  • Electricity cost: 10p/unit
  • Gas cost: 3p/unit
  • boiler efficiency: 83%
  • Central Heating is used: 8 months per year
  • CFL cost: £2.50
  • CFL lifetime: 8000 hours
  • filament lamp cost: 20p
  • filament lamp average life: 1000 hrs.
  • Electricity generating plant efficiency: 40%

Money Savings

Annual cost of use of one filament light:

  • 2x lamps @ 20p each = 40p for lightbulbs
  • 2000 hrs x 100w = 200kWh
  • 200kWh x 10p/unit = £20.00 for electricity

Total cost of operating one filament light fitting = £20:40 per annum

Annual cost of use of one CFL light:

  • 2000 hrs / 8000 hrs x £2.50 = 62p for lightbulb
  • 2000 hrs x 25w = 50kWh
  • 50kWh x 10p = £5.00 for electricity

Total cost of operating one CFL light fitting = £5:62 per annum

The CFL produces 25w of heat instead of 100w, so this extra heating effect of the filament lamp must be made up for by the gas for 8 months of the year.

  • 100w - 25w = 75w
  • 75w x 2000 hrs x 8/12 months = 100kWh.
  • At 83% boiler efficiency, 100kWh output requires 100/.83 = 120kWh gas use.
  • Cost = 120kWh x 3p = £3.60
  • Total cost of cfl use = £5.62 + £3.60 = £9.22 per annum.
  • Saving = £20.40 - £9.22 = £10.78

Saving = £10.78 per year per light fitting.

A household using 8 such fittings would therefore save in the region of £86 per annum.

Savings are higher in unheated locations.

With air conditioning

When a/c is used the savings for CFLs are greater.

Example: using the example above, plus:

  • AC use: 2 months per year
  • AC Energy extract/use ratio: 3:1
  1. 2 months CFL use uses 2/12 x 2000hrs x 0.025kW = 8.3kWh
  2. 2 months Filament use uses 2/12 x 2000hrs x 0.1kW = 33.3kWh
  3. Filament lamp thus uses an extra 25kWh over 2 months.
  4. This requires ac electricity use of 25/3 = 8.3kWh to extract it
  5. 8.3kWh @10p/kWh costs 83p

Thus each light fitting using a filament lamp costs another 83p in electricity to extract its heat. For a single bulb in centre of room this isn't much, but for multiple downlighter spot halogen lighting the amount adds up quickly. And this figure is on top of the savings mentioned above.

There's a second extra cost associated with filament lamps and ac as well. If you're using rooms full of halogen filament lamps, you need a bigger ac unit to get the same target temperature, meaning a higher purchase price. Or you use the same unit, run it for more hours and sit in a hotter room.

Offgrid use

Electricity for offgrid use is particularly expensive. It can cost as much as 50p per kWh. This makes the cost of running filament lamps far higher than CFLs. Linear fluorescent is popular off grid as it usually has even better energy figures than CFL.

Energy & carbon Savings

When not to use CFL

CFLs are not well suited to all applications.

Outdoor PIR lights

PIR lights switch the lamp frequently and for short periods. This causes premature failure of nearly all CFLs.

Cold outdoor weather means low initial light output and prolonged warm up periods, which gives poor results on a PIR light.

Outdoor CFLs rated to run down to freezing are available, but they still suffer low initial output with slow warm up.

Bathroom Lights

If a bathroom light is switched on frequently for very short periods, most CFLs fail early.

CFLs without filaments are immune to this issue, but cost more, and aren't often seen in supermarkets etc.

To replace linear fluorescent lights

CFLs work fine in place of linear fluorescent, but are usually not as energy efficient as them, so replacement doesn't yield any further savings. Linear fluorescent are the most energy efficient type of lighting normally used in homes.


CFLs are normally not dimmable. Ordinary CFLs work on a dimmer when left set to full, but if left on reduced setting the CFL's input resistor is likely to fry, ending bulb life.

There are 2 types of dimmable CFLs, those operated by a dimmer, and those that select differing brightness levels according to switch operation patterns. Cost makes them unpopular.


CFLs don't look anywhere near as nice, and don't produce the prismatic colour effects of filament lamps.

Some types of timer

A minority of timers pass neutral current through the lamp when off. With some CFLs this causes a regular momentary flash when off. Timers with a neutral connection don't cause this issue. See below for resolving this.

On very long switched wire runs

A CFL may flash occasionally when off if the switch cable run is especially long. See below for resolving this.


Poeple with photosensitivity can react badly to CFL light. Photosensitivty is caused by medical conditions such as Lupus and some medications. CFLS with an outer glass envelope over the tube don't cause this.


Distribution of light varies with lamp shape.

  • Pear shape gives fairly even light output.
  • Spiral & candle give some variation with more light out the side than end on.

Stick lamps give much more light out sideways than end on. This is an advantage with pendant fittings, where it produces more even light spread. It makes them ill suited to fittings that can only make good use of light from the front of the lamp, such as most spotlight fittings, and some downlights.

Occasional flashing

In exceptional cases a CFL flashes occasionally when switched off. This is due to wiring capacitance passing a tiny current, which gradually charges the CFL's reservoir capacitor, and after a while it attempts to start, giving a momentary flicker.

2 conditions tend to cause this:

  • an especially long switch wire run
  • supply switched on the neutral instead of live pole

Other than moving a neutral switch to the live line, possible solutions include:

Filament Lamp

Appliance lamp 4218-2.jpg

If a filament lamp is on the the same switch (or PIR/ timer) as the flickering CFL, the problem doesn't occur. The filament lamp can be low power, such as 15w, to minimise extra energy use.


One resistor 0982-12.jpg

It is also possible to stop the problem by fitting a suitable resistor in parallel with the bulbholder. Use either:

  • A 270k to 470k 400v rated resistor, or
  • 2x 150k to 220k 200v rated resistors in series, with both the same resistance value.

Resistor choice explained:

  • If using the common 200v 0.3w type resistors, they're only 200v rated, so 2 in series must be used, and of the same value so the voltage drop across each is equal.
  • A 270k resistor will dissipate 0.2w on 240v mains.


Capacitor 2756-4.jpg

A capacitor can be used in the same way as a resistor. These should not be fitted inside the lampholder itself for temperature reasons, but can fit in a ceiling rose, junction box, switch backbox or similar. Capacitors consume no power.

A 10nF 275vac capacitor with X2 dielectric is suitable.

Note that capacitors marked as 250v rated are totally unsuitable for mains use (but 250v ~ are ok). Before the advent of X & Y capacitor classifications, 600vdc caps were often used on unfiltered mains, but this is no longer compliant.

2 way switch

Many light switches are 2 way.

Live  ----o---
              o------ switched live line to lamp

Conventional use

                                    o---/\/\--- Neutral
switched live line to lamp  ----o---
                                    o------ Live

No-flash variation

R1 is a single 270k resistor rated to 400v, or 2 identical 150k 1/4w resistors in series.

Lamp type

A final option is just to pick a CFL that doesn't light instantly when power is applied. Some CFLs take half a second or so to start.

CFLs have other advantages

As well as saving money and energy compared to filament lamps, CFLs have characteristics that make them particularly well suited to some tasks.

Bedside lamp

Picking a CFL that comes on at reduced brightness initially, as a minority do, is a lot more comfortable on the eye than the instant full output of filament lamps.

Kids' room lamps

CFLs cause less fire risk than hot filament lamps. A knocked over plug-in light with a CFL is not a fire risk, and a CFL with something draped over it is very much less likely to cause a fire than a filament lamp.

Kids are not the most responsible and careful members of society, and their behaviour around plug-in lights is no exception.

Data supplied by the Department of Communities and Local Government, 11/02/10, suggest that in 2007 portable lighting appliances were responsible for 944 fires, of which 155 caused injury, and 4 resulted in a fatality.

Hot weather

With a/c

During air conditioning use, you pay twice for the extra power used by filament lamps. First the filament bulb uses more electricity, then the a/c uses power to extract that heat from the building.

Without a/c

When no a/c is in use, the heat of filament bulbs just goes to increase the indoor temperature further. How much further depends on the lighting setup, and varies. Temp gains can be as high as several C in some cases, particularly with halogen downlighting. A few degrees C has a fairly big effect on comfort.

Inspection lights

Small CFLs are generally more robust than filament lamps, though not by any huge margin. This may result in less bulb failures. If your use is rough enough to break either type of bulb regularly, LEDs are better.

Night lights

Long on-times suit CFLs well. Much lower run temperature also makes CFL less of a fire risk than filament lamps.

CFLs are readily available down to 3w, which cost very little to run (around £1.20/year for 9hrs every night).

Backup lighting

Long life and low power consumption make CFLs well suited to back up other lighting in areas where light failure would cause a problem. Inaccessible stair lighting is one such example, whether the main lighting is CFL, filament, or any other type.

See facilities lamp and electrodeless lamp sections

Special Purpose Lamps

High power Lamps

CFLs of powers upto over 100 watts are available.

Electrodeless Lamps

Electrodeless CFL Lamps have much longer lifetimes than standard CFLs, with life expectancies of 15,000hrs and up.

The Genura is an electrodeless R80 lamp with at least 15,000 hour life expectancy, and a £20 price tag to match. Even at these prices, total cost of ownership is still lower than filament lighting by a good margin.

Lamps with even longer life cost more.

Facilities Lamps

Extra long life lamps are available with lower price tags than the Genura, but in general you will pay a bit extra to avoid changing lamps as often. Life expectancies vary, but 12,000 or 15,000 hours is fairly typical. These are generally called facilities lamps, and are usually used in locations where there is a cost to relamping.

For domestic use these lamps are useful for locations where relamping is inconvenient. Examples include:

  • Lights mounted at a great height.
  • Shared entrance area lights
  • Lights where the occupant is unable to relamp, eg disabled or elderly.
  • Exterior light fittings that are not quick & easy to open (but not PIR lights).

Yellow CFLs

Yellow CFLs can be used outdoors to reduce attraction of insects. Yellow CFLs have an even greater energy efficiency advantage over yellow filament lamps.

Titanium Dioxide CFLs

Titanium Dioxide coated CFLs cause chemical reactions in the air touching the TiO2 coating. Water vapour is turned into hydroxyl radicals, which oxidise odours, and kill bacteria, viruses, & mould spores.

Blacklight CFLs

Black light bulb2.jpg

Blacklight CFLs are available for modest prices, and are an easy way to add a little style to parties. Also used to check bank notes and detect biological residues.

Never use germicidal UV lamps for this, these cause eye damage.

Colour CFLs

CFLs are available in many colours besides white, such as red, pink, orange, yellow, green & blue. While such lights are of limited use, the ratio of their energy efficiency compared to coloured filament bulbs is very much greater than 4:1, for reasons it is not necessary to delve into here.

Colour CFLs may be used for decorations, parties, etc.

A colour CFL fitted temporarily in the porch also makes it very easy for visitors to find your house - though red is best avoided for most of us.



CFLs continue to be less popular than filament bulbs despite the benefits. Reasons most often cited for this include:

  • not liking the light
  • lamp didn't fit in the light fitting

Other reasons include:

  • not liking the appearance of the bulb itself
  • can't be bothered with them
  • contribution to energy and pollution reduction too small to affect climate outcome.
  • money saving too small to care
  • appearance more important than savings
  • can't dim CFLs easily
  • higher level of premature failure in some applications
  • CFLs dont reach full brightness instantly
  • light output level drops more through its life than with filament lamps
  • safety concerns regarding mercury content
  • stated power equivalence on package untrue (true, but picking a genuinely equivalent lamp is hardly a challenge)

There are also some reasons sometimes cited that are either not really correct or not entirely logical:

  • CFLs can take a long time to reach full brightness when they are cold (few CFLs behave like this today.) This still happens where unsuitable types are used outdoors)
  • safety concerns regarding fire hazards if the ballast shorts out (ballasts contain a failsafe safety device for this. Total fire hazard is less than that of filament bulbs)
  • higher bulb cost (while true, the energy savings are greater than the added bulb cost)
  • not knowing if they really save energy (they do)
  • not knowing if they really save money (they do)

Medical conditions

People with photosensitivity, notably those with Lupus, may have a severe skin reaction to UVA light emitted by some CFLs. This applies to people who need to avoid daylight, which also contains UVA. CFLs with an outer glass cover over the tube don't cause this problem. Ditto CFLs in enclosed glass light fittings.

Faulty CFLs can trigger epileptic seizures in epileptics intolerant to strobing. However

  1. such a failure mode is very unusual
  2. a dying lamp that was flashing would normally be removed from service immediately by any homeowner.


CFLs do contain a trace of mercury, which is released on disposal or breakage if the lamp is not recycled. Burning coal to produce the extra power used by filament lamps releases more mercury than the mercury contained in a CFL lamp, but the mercury released by burning coal is not concentrated in one's living space. Reference

Filament lamps contain thorium, another toxic heavy metal, but it doesn't create a significant risk on breakage.

Mandated CFLs

At one time the government mandated the fitting of CFL-only light fittings in new builds, and these fittings were in most cases promptly removed. The only thing left is resentment at the waste of the exercise.

Some supported this policy on the grounds that at least some energy efficient fittings are left in service. However the fittings mandated couldn't take the popular low cost type of CFL.


Bulb Choice

Available lamp models change, so try one each of a few different ones to see which gives best results.


Like linear fluorescents, CFLs come in more than one type of white. Most are 2700K or warm white, and are equivalent to filament lamps. Daylight lamps give a much colder light not liked by most people.

Colour temperature may be indicated in any of 3 ways:

  1. Kelvin figure. 2700K - 3000K is warm, 4500K is cool, 6800K is very cold.
  2. Kelvin temp and CRI may be encoded into one figure. 827 means 2700K with a CRI in the 80s%, 854 means 5400K.
  3. Colour names such as warm white or daylight. Daylights give a very cold light, and are rarely appreciated.

If you have an unmarked lamp, the simplest way to check is to put 2 bulbs side by side, a filament bulb and the cfl, to see if they give the same light colour. Some give an accurate match, some are slightly pinkish, and some give a much colder light. Most people prefer bulbs that match filament lamps.

Outdoor Use

CFLs take time to warm up in winter outdoors. Outdoor rated bulbs are available. These often have glass or polycarbonate outer covers.


For R80 fittings where the bulb is not visible, ie is wrapped around by the fitting cowl, try using miniature non-R80 bulbs. GE's microspirals fit well. For some reason R80s are either steeply priced (Genura at around £20 each) or not as attractive as filament R80s. Despite the price tag, even the long lived Genuras save money in the end.

20w Bulb Orientation

CFLs of 20w and more are designed to be used base down. They can be used base up too, eg in ceiling pendant fittings, but some types have shorter lives than rated in this position. This does not prevent them saving money and energy though, as the energy saving is far greater than the bulb cost.

Enclosed Fittings

Most CFLs are happy enough in enclosed fittings, but a minority aren't. Sometimes light output falls, or the bulb fails early.

Fitting Power Ratings

Generally you don't need to worry about fitting power ratings when using CFLs, as the CFL power rating is far below the fitting's limit. But with enclosed fittings or fitings where you need to squeeze maximum light output, its best considered to avoid bulb failures.

A 25w rated bulb holder can cope with anything upto 25w of lightbulb, regardless of what technology that bulb uses.

But a 25w CFL would get too hot in a 25w max rated fitting, because CFLs are designed to run cooler than filament bulbs. So the practical recommended limit for CFLs is below the light fitting rated max. Its impossible to provide an exact number, as heat tolerance varies among CFLs.

If your fitting isn't giving enough light with a filament bulb of max rated power, using a CFL of half the power provides a lot more light.

If too high a power CFL is used, the bulb runs hot and fails early. However this is not the fire risk that too high powered filament bulbs present, its only a risk to the lifetime of the bulb.

Some CFLs give reduced light output when run too hot.

User Reviews


  • Light quality excellent
  • bulbs reliable
  • 20w+ bulbs achieve full rated life when operated cap up
  • recommended
  • 10/10


  • Light quality good
  • Candle bulb glass covers break easily
  • 8/10


  • Light quality so-so
  • Reliable
  • Good power/size ratio with mini spirals
  • 7/10


  • Bulb life unimpressive
  • 5/10


  • Light quality a horrendous 6800K
  • Light output started a bit low, and declined badly
  • 1/10

Screwfix R80s

  • Lower light output than 60w R80 filament bulbs
  • Light quality so-so
  • Slightly longer bulb looks bad in fittings where the bulb is visible.
  • High price
  • 4/10

Megaman ultra compact candle

These are designed to act as a replacement for candle effect bulbs, and are very similar in shape and overall size.

  • 7W bulb gives similar light output to a 40W filament when looking at the bulb, although a reduced output into the room. A recent test on a couple of these lamps after they have been in use for 2 years, shows light incident on a surface about 6' below a three way lamp fitting, with two bulbs fitted at 14 Lux (when the lamps are fully warmed up). The addition of a new 40W incandescent bulb to the pair of CFLs raised the total light level measured to 36 Lux, suggesting that the useful light output from each CFL is only 1/3rd that of the incandescent. This is obviously a slightly harsh test since it compares old CFLs with a new incandescent.
  • Light quality is a fairly good match in both brightness and colour
  • Warm up is reasonably quick
  • Price approx £6 / each
  • 7/10

GE Spirals

  • High efficiency due to 8mm tube
  • Good light quality from the 2700K ones
  • Unpleasant light from daylight ones
  • Short length makes them usable in R80 light fittings where the wider beam is acceptable
  • 15w bright enough to replace 60w filaments
  • £2.28 at Tesco and half price offers frequent - but check you get 2700K
  • long life & no premature failure problems, despite operating cap up
  • 9/10

Tesco large candle

  • Probably made by GE - but not all boxes carry a brand
  • Slightly green light quality
  • Slowish warm up
  • Colour match between bulbs seems poor - identical bulbs bought at the same time and used in the same multi lamp fitting have never looked the same.
  • Longevity: - first one failed in about 1.5 lifespans of a filament lamp operating cap down.
  • 3/10

Tesco 11W Stick Lamp

11W Stick lamp - click to enlarge
  • better than normal output toward the red end of the spectrum, giving better colour rendition than most CFLs
  • Warm up is not too slow, and the initial light output is usable.
  • Colour accuracy between bulbs is good.
  • Claimed equivalence to 60W is not actually too far off with these.
  • 9/10

Tesco Stick Lamps

I bought some in about Feb 2008 (priced 10p). By Nov 2010:

  • Big fat 3-stick one in the lounge was still in use last month, with fairly heavy use.
  • Short 3-stick ones still in use and fine in the bedroom, with moderate use
  • SES reflector spotlights in the kitchen started looking a bit dim, moderate use but switched on and off a lot.


For a list of suppliers, see Suppliers Article.

See Also

Dollar store CFL review, many problems Unusual CFLs