Fluorescent Lighting

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 1930's. 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 1950's, 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 1970's, 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:

1. Hidden fittings & hidden bulb.
2. Uplighting
3. comfortable light level.
4. No flicker or flash
5. 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.
6. Tubes of a size that makes keeping a spare practical.

For 1 & 2 - use trough fittings.

For 3 - Choose around a quarter the power you would use with filament bulbs.

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 clean fresh and slightly cool look. These are my favourite halophosphate tubes for domestic lighting.

4000K look cold and anaemic, 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 & 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, depending on manufacturer, all of which look the same.

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

All are a (normally) plastic can with a 2 pin base.

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). Electronic versions don't keep trying to start a dead tube.

Thermal starters were used before the glowstarter took over in the 1950's. Thermal starters have 4 pin bases. They start after a delay with no flashing, but take longer. If the light is switched off for a second they will generally not relight straight away. 4 pin starter cans continued to be produced during the 1960's for replacement purposes, but contain a glowstarter instead.

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 it's not used in the UK.

Can I re-use my scanner/monitor CCFL

These can be reused for house lighting, but there are 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 usually 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 give 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.

More

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

See Also

Rewiring Tips

Discharge Lighting

Suppliers

CFL Lamps