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  • Compact Fluorescent Lamps (CFLs) save power consumption and carbon emissions compared to filament bulbs.
  • 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, from excellent to awful.
  • CFL lighting does not save a lot compared to other ways to save energy & money, but its usually an easy option that saves quickly.
  • Some people don't like the look of CFLs
  • The energy and cost savings are not big.

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.

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

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 will 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 filament light fitting = £5:62 per annum.

The CFL produces less heat (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% 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.

Energy Savings be completed another time

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 will cause premature failure of CFLs.

Cold outdoor weather will mean reduced light output and prolonged warm up periods, which will give poor results on a PIR light.

Bathroom Lights

If a bathroom light is switched on frequently for very short periods, the CFL will fail early.

To replace linear fluorescent lights

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

Some types of timer

A minority of timers pass neutral current through the lamp when off. With CFLs this will cause a regular momentary flash when off. Timers with a neutral connection do not cause this issue.

See below for resolving this

On very long switched wire runs

A CFL may flash occasionally when off if the switch wire run is especially long.

See below for resolving this

Occasional flashing

In exceptional cases a CFL will flash 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 attmpts 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

If a filament lamp is on the the same switch (or PIR/ timer) as the flickering CFL, this problem will not occur. The filament lamp can be a low power type, such as 15w.


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.


A capacitor can be used in the same way as a resistor. These should not be fitted inside the lampholder itself for temperature reasons. 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. Before the advent of X & Y capacitor classifications, 600vdc caps were often used on unfiltered mains, but this is no longer compliant.

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

Use of CFLs in plug-in lights in kids' rooms saves lives.

CFLs are not the fire risk that hot filament lamps are. 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.

In the UK in 2001 there were 69,000 house fires, with 613 fire deaths. An unknown percentage of these are caused by plug-in lights.

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 lighting. 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, filament bulbs are cheaper to replace.

Night lights

Long on-times suit CFLs well. Much lower run temperature makes CFL less of a fire risk than filament lamps, which is especially useful for plug in lights used at night.

CFLs are readily available down to 3w, which cost so little to run (around £2.50/year for all night use) that these can be freely used for night lighting.

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.

Special Purpose Lamps

High power Lamps

CFLs of powers upto over 100 watts are available.

Eurobatteries is one such supplier.

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

Blacklight CFLs are available for quite modest prices, and are an easy way to add a little style to parties.

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 - although 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 changes more through its life than with filament lamps
  • safety concerns regarding mercury content
  • stated power equivalence on package untrue (this is a fair point, 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 (this was an issue with early types, and is still an issue 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

Those people who show photosensitivity, notably those with Lupus, may have severe reactions to UVA and UVB light emitted by some CFLs. This applies to people who need to avoid daylight, which also contained UVA and UVB. Faulty CFLs can trigger epileptic seizures in epileptics intolerant to strobing.


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 might release 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.

Filament lamps contain thorium, another toxic heavy metal.


Mandated CFLs

Many people object to the government mandating the fitting of CFL-only light fittings in new builds, and these fittings are in most cases promptly removed. The only thing left is a sour taste, and resentment at the waste of the exercise.

Some support this policy on the grounds that at least some energy efficient fittings are left in service.


Bulb Choice

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

Put 2 bulbs side by side, 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. Usually people like bulbs that match filament lamps best.

Outdoor Use

Most CFLs will take a while 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. 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 will have shorter lives than rated in this position. This does not prevent them saving money and energy.

Enclosed Fittings

Most CFLs are happy enough in enclosed fittings, but a minority aren't, and light output may fall, or the bulbs fail earlier than usual.

Fitting Power Ratings

Generally you don't need to worry about fitting power ratings when using CFLs, as the CFL power rating will be far below the fitting's limit. But with enclosed fittings or fitings where you need to squeeze maximum light output, this is 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 different CFLs will tolerate differing heat levels.

If your fitting is not giving enough light with a filament bulb of max rated power, using a CFL of half the power will provide a good deal more light.

If too high a power CFL is used, the bulb will run hot and fail early. However this is not the fire risk that too high powered filament bulbs present, it is simply a risk to the working life of the bulb.

Some bulbs may also produce 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
  • bulbs reliable
  • Good power/size ratio with mini spirals
  • 7/10


  • Bulb life poor
  • 5/10


  • Light quality horrendous
  • Light output starts a bit low, and declines 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


For a list of suppliers, see Suppliers Article.

See Also