Fluorescent lighting is the most energy efficient lighting suited to widespread domestic use.

Fluorescent lighting can look good if chosen and installed well. But the all too common choice of a bare bulbed butt ugly glowstart fitting in the centre of the room with a tube chosen at random is a recipe for unpleasant lighting.

Types of fluorescent lighting

Linear fluorescent have been with us since the 1930s.

Circline tubes are a variation on the theme popular in the 1960s, and occasionally still used in homes.

Miniature tubes have found use in emergency exit signs, torches, and small displays.

HO high output and VHO very high output tubes are used in aquaria where high lighting density is required. These tubes have lower efficiency than standard tubes.

CFL compact fluorescent lamps are thinner tube lamps which run at higher output than traditional tubes. They are commonly found with integral ballasts in the bulb base designed to replace filament bulbs, but are also available to run from separate ballasts in the luminare.

CCFL cold cathode fluorescents are very thin tubes that backlight LCD monitor & TV displays. CCFLs are also used in scanners.

History

The first installation in the UK was in a London Underground station in the 1930s. During WWII, fluorescent lighting was installed in many factories to help the war effort. These were all 5' 80W T12 (1.5" diameter) tubes, which used the same ballast as an 80W mercury vapour lamp and bayonet cap tube connectors, as these parts already existed at a time when manufacturing new parts was to be avoided where possible. 6' and 8' tube sizes followed.

In the 1950s, a 2' 40W tube for street lighting and the lower power-per-foot 4' 40W tube were introduced, and the 5' tube was reduced to 65W which resulted in more efficient operation. The new tubes were all bi-pin connectors, and the older tubes migrated to bi-pin connectors too. Glow starters replaced thermal and manual starters.

In the late 1970s, Thorn Lighting developed the lower power 8' 100W tube to replace 8' 125W tubes with only a tiny drop in light output. There followed replacement lower power tubes for all the other popular tube lengths, also intended to run in the original fittings with the same series ballasts. The 8' 100W tube is a T12, but all the other reduced power retrofit tubes are T8 (1" diameter).

In 1980, Philips introduced the SL18, the first integral ballasted compact fluorescent retrofit designed to replace a filament bulb. Thorn Lighting followed with the 2D compact fluorescent for the same purpose, but the tube and ballast were separable to enable tube and starter replacement without discarding the ballast. Compact fluorescents have always suffered from being larger than their GLS equivalents, but over the intervening years, this difference has reduced, meaning more light fittings can take compact fluorescent retrofit lamps.

Lamp sizes

T-values identify the tube diameter in 1/8ths of an inch, so T8 is a 1" diameter tube. Some other European countries specify T-values in millimetres instead, and sometimes these values are seen on packaging.

Common British tube sizes include:

8' 125W & 100W (both T12)
6' 85W T12 & 70W T8
5' 65W T12 & 58W T8
4' 40W T12 & 36W T8
2' 18W T8
21" 13w T5
12" 8w T5
9" 6w T5
6" 4w T5

Note that new fittings have not taken T12 tubes (except for the 8' 100W) for many years now, although T12 tubes remain available for older fittings.

Less common tube sizes include:

6' 75W T12 (obsolete)
5' 80W T12 (power rating of 5' tubes prior to 1960)
3' 30/33W T12
2' 20W T12
21W

New ranges of T5HE (High Efficiency) and T5HO (High Output) tubes are commonly used in new commercial luminares, but not in domestic situations as yet.

T4 tubes are commonly used in domestic situations for things like under-cupboard lighting, but the tube lengths and power ratings are not standardised between manufacturers.

Good fluorescent lighting

Good fluorescent lighting needs the following points:

Hidden fittings & hidden bulb.
Even well distributed lighting
Comfortable light level.
No flicker or flash
A tube of respectable quality. I like 3500K tubes, there are several good types to choose from, but there are also many unpleasant or poor light quality types of tube on the market.
Tubes of a size that makes keeping a spare practical.

For 1 & 2 - Trough fittings (uplighters) achieve both.

For 3 - Fluorescents are around 4x as energy efficient as filament bulbs, so a quarter the power of comfortable filament lighting is a good starting point.

For 4 - An electronic ballast fitting avoids all the flicker and flash of cheap glowstart fittings.

For 5 - see the next section

For 6 - 2 foot tubes are easiest to store, 4' are next best. I would not usually recommend larger tubes for domestic use.

Fluorescent Tube Types

There are many different versions of white, ranging from excellent quality to dire. Buying tubes at random can give you unsatisfactory lighting.

Tubes are normally marked with their colour on on the glass at one end. Many shop assistants are unaware that there are different versions of white, or that the tubes are thus marked.

The Many Different Whites

Tubes marked simply as white are not of the best quality, though not the worst.

I can recommend 2700K and 3500K tubes, but I don't recommend higher colour temperature tubes for household use.

2700K is the colour of GLS filament bulbs, so it matches perfectly with traditional filament lighting. 2700K is a warm slightly yellowy white.

3000K is the colour of halogen bulbs, cleaner and crisper than 2700K. Some 3000K tubes don't have good CRI*, so if you want 3000K to match halogen its best to pick the more expensive triphosphor tubes rather than halophosphates.

3500K will not match other light sources, unless they're also 3500K fluorescent, but used alone they give a fresh clean look. These are my favourite tubes for domestic lighting.

4000K look cold and anaemic to most people (though there are some that like them), and 4500K and up are like the old fashioned 'cool white' tubes that once gave fluorescent lighting such a bad reputation. There are also proprietary numbering systems, such as the Philips system.

Cool white and daylight are ill suited to domestic use.

Phosphor types

As well as the different shades of white, there are 2 phosphor families in use today: halophosphate and triphosphor.

The older halophosphate tubes come in many versions of white, and have a wide range of CRIs from the 50s (grim) to over 90 (excellent).

T8 Triphosphor tubes have consistently higher CRI than halophosphate (80s to 90s), slightly higher lumen output per watt, and output doesn't reduce as much over time as halophosphates. These tubes also cost more.

CRI = colour rendering index, a measurement of how well fluorescent tubes render colour. 100 is perfect, 50 is bad.

Fitting Types & Installation Methods

Trough

The trough encloses both tube and light fitting in a trough, so neither are directly visible. The trough is open at the top for uplighting, or the bottom for downlighting.

Uplighting troughs are a very good general purpose lighting method, giving excellent results in most cases for general purpose lighting. They can provide relatively even lighting, and avoid all glare & bright areas. They work very well in domestic sized rooms, and also in larger spaces with a high ceiling.

Uplighting troughs give the best light spread if the trough is moved away from the wall a bit. Small troughs with tubes close against the wall tend to highlight plaster imperfections and create high brightness patches.

Downlighting troughs are useful where it is desired to restrict the light output to a limited area.

Shelf

The fitting is sat on a shelf, turned with the tube facing the wall so the tube is not directly visible.

The quality of light spread is as good as the trough fitting, with relatively even uplighting and no glare. But the fitting itself remains visible, and they are generally not designed with aesthetics in mind.

A good option for lighting in garages, workshops, etc. The shelf will need dusting now and then.

Downlighter

Ceiling mounted downlighters are popular in office and retail premises. They come in surface mount and flush recessed types. They are well suited where high illumination levels are required, and clean white or near-white flooring is used. Other flooring colours wil result in significant reduction in energy efficiency.

They are not well suited to home use since they put out a lot of light over a limited area only.

Bare & basic

A bare tubed light on the ceiling is a basic way to use fluorescents, and is popular with nonprofessional installs. It works but is not one of the better options. Lightspread is not great with shadows all round, the bare tube creates glare, and the ugly fitting is visible and brightly lit.

Diffuser

Diffusers improve the appearance of fittings, but are generally not very good at eliminating glare. A bare bulb covered with a diffuser is not one of the best options.

Shadowless

Installing bare fluorescent lights in several continous lines was for decades a preferred method for rooms where people work at desks. It is a simple way to provide very little shadow on the work. This is a minimum cost way to install fluorescent lighting for work, but is now mostly replaced by more modern methods.

Glare can be quite bad with these installs. Reflectors may be fitted to greatly reduce this problem.

One of the minor advantages of this approach is that the light from adjacent fittings mixes well, so it works acceptably with a mixture of tube types. The old method of mixing different tube types to improve the spectral output can be used, but with the ready availability of good quality tubes this is no longer necessary or even desirable.

This method remains a fairly good choice for minimum cost work areas where the cheapest fittings and tubes will always be used.

Above cupboard

Low power lights fitted above kitchen cupboards can contribute a good amount of light to the room while keeping the fittings and tubes not visible.

These are effectively shelf fittings. Their weakpoint is that the cupboard tops need dusting otherwise light output drops. They are also not suitable for use with low ceilings, as the tubes would then be visible from across the room.

Under cupboard

A very effective way to light kitchen worktops. Don't overdo the light output.

A switch on each fitting enables some variation of lighting level after fitting. Putting every other fitting on a 2nd lightswitch makes a more relaxed comfort lighting level available at the press of a switch, also improving energy efficiency.

A dimmer enables good control of light level, but the dimmer and fittings must both be compatible with each other, and this will add a little to the price.

Single Long Tube

It is possible to use a single long tube for under cupboard lighting instead of several small ones. This can improve reliability and cost, and give perfectly even lighting at all light levels. However a dimming system is a must, as the full output power of a long T8 tube will be far in excess of what is required.

The tube should be mounted to the cupboard underside with clips, and the control gear housed in a separate box. Standard ceiling fittings are too bulky.

Disguised Supplemental Lighting

The idea of this is to provide part of the room's light without the fluorescent lighting being seen. One possible example of this would be a circline tube fitted in the ring of a filament bulb chandelier.

This approach retains the appearance of non-fluorescent lighting while providing some of the energy efficiency and reliability advantages of fluorescent.

Ballast Types

Note: North America uses the same names in many cases to mean completely different things from rest of the world. UK/International terminology is used here.

Switchstart

Switchstart is the most popular ballast type in Britain and most other countries with 220/240V mains. They are easily identified by their starting behaviour, they usually flash a few times during starting.

Switchstart fittings use a plug-in glowstarter. Fittings for domestic use sometimes have the starter under the removable panel, as starters rarely fail unless the fitting is left operating with a dead tube in it for a long time. In commercial environments where this does happen, the starter will often be replaced at the same time as the tube.

There are a few different ratings of glowstarter, all of which look the same. The ratings for each vary between manufacturers. Common ratings are:

4-65W and 4-80W for general purpose use.
4-20w glowstarters for the lower power tubes only
100-125w glowstarters for 8' tubes only
Series starters for fittings that run 2 tubes in series. These are sometimes marked as 110 / 120v / 110-130v starters.

All are a (normally) plastic can with a 2 pin base. Metal starter cans are decades old.

Electronic replacement versions are available which are a direct swap, and also available in wire-ended versions for wiring into the fitting (as they don't wear out). Most electronic versions don't keep trying to start a dead tube.

Thermal Starters

Thermal starters are visually better than glowstarters, as they avoid any flicker and flash during starting. They were used before the glowstarter took over in the 1950s. Thermal starters have 4 pin bases. They start with no flashing, but take longer than glowstarters. If the light is switched off for a second they will generally not relight, they need a very brief cooling off period first. 4 pin starter cans continued to be produced during the 1960s for replacement purposes, but contain a glowstarter instead. The original thermal starters consume around 1w during running.

Electronic

There are various types of electronic ballast. All start with no flashing. Pre-heat will heat the filaments for something between 0.5 and 1 second before striking the tube, and Instant start will strike the tube pretty instantly (manufactures usually specify < 0.1seconds). (Unfortunately, the term "Instant Start" is also used sometimes to refer to any type of electronic control gear, so you must check manufacturer's data sheet if you really want an instant start ballast.)

All the minature T4 and new T5HE and T5HO lamps can be driven only by electronic control gear.

Other Magnetic Ballast Types

There were also a number of types of starterless ballasts which were used before electronic ballasts became viable. They were mostly used in commercial installations, rather than in homes, as they were more expensive.

SRS (Semi-resonant start), invented by Thorn Lighting, uses a double wound transformer and essential circuit capacitor. The tube lights up steadily over about 5 seconds without flashing, just like a light being brought up on a dimmer. It was particularly suitable for low temperature (outdoor) use with the longer tubes, but cannot be used with the shorter tubes. (T8 replacement tubes should not be used with SRS ballasts.)
Quickstart, use filament heating transformers. The filament heating supply is reduced when the lamp lights. They light similarly to SRS, but typically in a second. The quickstart filament transformer is often a separate unit from the ballast, but the two can be combined in one can in other cases.
Rapid Start, use filament heating transformers. The filament is continuously heated. They light similarly to Quickstart. Rapid Start ballasts (sometimes referred to as dimming ballasts) can be dimmed with special dimmers if the filament transformer supply is separate from the tube current supply.
Instant start, is mentioned only for the benefit of US readers to say its not used in the UK.

CFL Ballasts

These are electronic ballasts, and working ballasts can be reused to run T8 or T12 linear tubes. They are designed as disposable items, with shorter lives than ballasts designed for linear tubes, but separating ballast from tube runs them much cooler, and prolongs their life greatly.

Capacitor Ballasts

Capacitor ballasts are found in workshops using rotating machinery. They are like glowstart fittings except that the choke ballast is replaced by a capacitor ballast, plus a small choke to reduce the crest factor (high peak current) inherent in capacitive ballasts which causes rapid wear of the tube electrodes.

They produce light out of phase with standard choke ballast lights. Choke and capacitor ballast circuits are used side by side, known as lead/lag pairs, to minimise 100Hz flicker, and thus eliminate the risk of strobing on rotating machinery, which can in some cases to a limited extent give the impression that a moving machine might be stationary. Leag/lag pairs (developed by Thorn Lighting) can either be supplied as twin lamp fittings with one tube on a capacitive (leading) ballast and the other on an inductive (lagging) ballast, or as a packing carton of single lamp fittings which are mixed, half capacitive, half inductive. Circuits using lead/lag pairs do not require power factor correction capacitors with the inductive ballasts as the capacitive ballasts cancel out the phase shift of the current.

The drawback with capacitor ballasts is the high crest factor (a current peak is dumped through the tube every half cycle when the gas discharge starts conducting and suddenly has to change the charge in the capacitor). This is why a small ballast is still required, to limit the current peak and reduce the bad effect on tube life. Electronic ballasts are preferred to lead/lag pairs now.

These is one version of capacitor ballast that does not seem to reduce tube life much. This is a capacitor ballast for 240v 2' tubes. A low power tube runs at relatively low voltage as well as using a relatively high capacitor impedance, and for both those reasons the current dump is smaller than with higher power tubes. Many 2' tubes will light with no starter, and can happily run in a fitting containing nothing but a series capacitor. Starting is slower than with glowstart, with light output ramping up during start.

Hybrids

Finally there are hybrid systems sometimes found, typically retrofits from the late 1980s. These are conventional iron electromagnetic ballasts with electronic starters. Performance varies depending on the design of the starter. Many are good, but the behaviour of the worst can be fairly unpleasant.

Energy Efficiency of Fittings

Old electromagnetic ballasts ran hot, typically dissipating around 10% of lamp power. It is no longer permitted to sell these.

New electromagnetic ballasts are required to meet band A efficiency, with much lower energy loss than in the past.

Electronic ballasts of all types are the most energy efficient. They also operate the tube at high frequency, producing a slight increase in tube efficiency.

Obsolete thermal starters, rarely seen now, consume around 1w watt during running. This is in addition to the electromagnetic ballast losses.

Energy Efficiency of Tubes

Tube Length

Energy Efficiency varies depending on tube length. Large tube sizes are more efficient, but they produce too much light for most domestic situations, resulting is nothing but unnecessary energy use.

Large tubes may be suitable for large high ceiling rooms, and areas where lighting quality is a low priority, such as garages.

Phopshor

Triphosphor tubes give slightly higher output than halophosphate. Halophosphate output declines significantly over time.

White vs White

Energy efficiency differs from one tube type to another. Cooler tints of white are generally slightly more efficient than the warmer tints. For domestic use this small difference is trivial compared to light quality, and light from cool tubes is considerd unpleasant by a lot of people. The slight extra efficiency (or technically efficacy) is one reason why cool tubes are still in widespread non-domestic use.

Colour

Most colour fluorescent tubes are made by using only one colour of phosphorescence. In other words all the light output is produced as the wanted colour. Contrast this with coloured filament lighting, where white is produced, then most of this light is filtered out, giving a heavy drop in total light output.

Consequently coloured fluorescent lighting is more energy efficient than filament by an even greater margin than comparing white light.

There are also colour tubes that are white with a colour filter layer. These still have much greater output per watt than filaments, but not by the even greater extent of the above type.

Output also varies significantly between colours. Displays of assorted colour tubes show a wide variation in perceived brightness.

Dimming

This section will deal with domestic dimming, as other methods are not useful for DIY. This section only covers present technology, as earlier methods (such as variacs & salt water tanks) are so rarely encountered, and unsuitable for installation today.

Dimmers

Most fluorescent fixtures are not compatible with dimmers. Dimmable fixtures are available, but both dimmer and light fitting must be compatible with each other.

Dimming produces a small drop in energy efficiency, meaning that reducing light level does save significant energy. This is in sharp contrast to filament bulbs, whose energy efficiency plummets rapidly on dimming.

Generally speaking, and it is only possible to be general on this, dimming fluorescents will save more energy and money than the dimmer costs and took to make, making dimmable electronic fittings a good choice on energy, money and comfort grounds.

Dimming does not prolong tube life.

Switchbanks

Switchbanks are an alternative to dimmers and dimmable ballasts, with lower cost and excellent money & energy payback. However these are sometimes inconvenient to retrofit. Where practical they should be fitted, since their utility and payback are both many times their very small extra cost.

Switchbanks can be anything from a 2 gang switch to a whole panel of switches, one for each fitting.

Both

Switchbank and dimmer may be combined if wished. The lower cost option is the dimmer feeds the switchbank which feeds the individual lights.

Tube Life

Tube life depends on type of ballast (& starter where used), and how often the tube is switched on and off.

Ballasts

Most electronic ballasts give the longest tube life, though ones that strike the tube in under a second will reduce tube life. Tubes are typically rated at 20,000 hours on electronic gear.

Glowstart fittings with iron ballasts typically give in the region of 10,000 hour tube life.

Thermal starters give longer tube life than glowstarts. Exact figures are not to hand, but given their behaviour it seems likely they will produce a tube life expectancy closer to electronic ballasts than to glowstart fittings.

Light Output

Light output declines over time, and in commercial installations tubes are routinely replaced before they die, for 3 reasons:

To maintain energy efficiency
Replacing all at once is much cheaper in labour than replacing them one at a time as they die
Avoiding the high failure rate near end of life also eliminates the regular appearance of dead or malfunctioning light fittings, which would look bad in retail premises.

Triphosphor tubes suffer much less output reduction than the older halophosphate technology, so the most economic method of running these is to give them a longer service life than with halophosphate tubes.

Wiring

There is one gotcha when wiring up used fluorescent fittings. Most older ballasts run hot, and standard pvc insulated wire must not be routed over the iron ballast. Most switchstart fittings either used high temp internal wiring where it passed over the choke, or used a shielded channel to keep the wiring cooler.

Fluorescent lights must always be earthed, they should not be connected to historic 2 core lighting circuits. Most fluorescent fittings generate starting voltage pulses well above mains voltage.

Can I re-use my scanner/monitor CCFL?

In principle these can be reused for house lighting, but there are many issues with them:

Lamps should be protected from touching, as the high frequency high voltage will pass through the plastic wrap to humans.
The original ballasts mostly run on 12v and contain logic for on/off control. If powered they may keep the lamp off by default, so you may need either to apply a signal or slightly hack the ballast to get it to light.
CCFLs for these apps typically use a very high colour temperature tube, which gives a very cold looking light.
The tubes are generally low power
The tubes are typically around a foot long, which makes them less versatile than CFLs.
Some CCFL tubes run very hot, particularly at the ends, and could ignite any flammable material in contact or close by.

Other Fluorescent Lamp Types

This article addresses domestic lighting. There are other types of fluorescent lamps, such as

blacklight (UV)
blacklight blue (UV)
grolux
germicidal (UV)
inductively driven electrodeless lamps
microwave driven electrodeless lamps

To Do

lpf & hpf

outdoor use

disposal

ballast terminology: iron, wound, choke, ballast,

electronic fittings explained: tron ballast vs tron starter + iron ballast.

plant liting

Fluorescent Lighting