Buying Guides - Light Fitting Types - Fluorescent Fittings
Published: July 26, 2011
When it comes to general lighting, fluorescent lamps have been popular since the 1950s. Nowadays, fluorescent tubes are commonplace in factories, schools, workshops, garages and in some parts of the home.
Compact Fluorescent Lamps (CFLs)
A relatively modern fluorescent fitting that is becoming increasingly widespread is the compact fluorescent light bulb (CFL). With many compact fluorescent lamps, the auxiliary electronics are integrated into the base of the lamp, which means they can be used in standard light bulb socket.
Fluorescent light bulbs come in many shapes and sizes. They are identified by a standardised coding system that reveals valuable information about operating characteristics and physical dimensions. One key factor is a tube's diameter, and this is given by the number following a 'T' (which denotes 'tubular'). The figure refers to the tube's diameter in 1/8ths of an inch, so, for example, a T8 tube would have a diameter of 1 inch.
T5 Fluorescent Tubes
The light output of T5 fluorescent lamps per unit length is almost identical to the larger T8 lamps. T5 lamps cannot be used as replacements for T8 lamps as they are slightly shorter. However, some luminaires can be adapted to accept either T5 or T8 lamps by changing the sockets and ballasts. The T5 is a versatile and effective source of illumination that is ideal for factories, schools, offices, supermarkets, underground railways etc.
By using rare-earth phosphors, T5 fluorescent lamps achieve improved colour rendering and high efficacy. The correlated colour temperature (CCT) and colour rendering index (CRI) of the lamps is determined by the phosphors used in the manufacturing process. The CRI of T5 lamps can be specified from 70 to the mid-90s. For good quality lighting it is advisable to specify a CRI of at least 80.
T5 lamps require special ballasts. These allow T5 lamps to operate at frequencies greater than 20 kilohertz and offer such features as instant start, rapid start and programmed start. In most cases, the T5 ballasts will not work with T12 or T8 lamps.
T5 HO lamps
'HO' stands for high output. T5 HO lamps produce more light than standard T5 lamps and are obtainable in higher wattages. HO lamps are available in the same diameter and length as standard T5 lamps.
T8 Fluorescent Tubes
The 32W T8 fluorescent lamp is becoming the standard for new construction and a replacement for 40W T12 fluorescent lamps. T8 lamps are easily available in a selection of straight and U-shaped designs. Compared to T12 fluorescent lamps, T8 lamps have the same 20,000 hour life expectancy and 32% lower typical energy usage, making them an ideal choice for offices, task lighting, schools, conference rooms, halls and retail outlets.
T8 fluorescent lamps achieve both improved colour rendering and high efficacy by employing rare-earth phosphors. The correlated colour temperature (CCT) and colour rendering index (CRI) of the lamps is determined by the phosphors used in the manufacturing process. As with T12 lamps, T8 lamps are obtainable in a range of colour temperatures, including:
- Warm (3000 K)
- Neutral (3500 K)
- Cool (4100 K)
- Very Cool (5000 K)
'Full Spectrum' lamps are usually 5000K or more, and emit 10 to 20% of their output as UV light. The CRI of T8 lamps can range from 70 to as high as the mid-90s. For great lighting quality it is advisable to specify a CRI of at least 80.
T8 fluorescent lamps require an electronic ballast that are designed specifically to operate lamps at a lower current than T12 lamps. When T12 lamps are replaced with T8 lamps, therefore, the ballast must also be replaced. The advantage of electronic ballasts is that they don't flicker or hum and they use less energy than conventional ballasts.
T12 Fluorescent Tubes
T12 fluorescent lamps have traditionally been the most commonly used fluorescent tubes and have been installed in millions of homes, offices, retail outlets and schools. Although it was considered energy efficient in the 1970s, the T12's reduced life expectancy, poor colour rendering and low light output often meant that more lamps and fixtures were usually needed, which generally offset the energy savings. At present, existing 40W T12 fluorescent lamps tend to be replaced by the more effective and more efficient 32W T8 fluorescent lamps.
Wide Range of T12s
The length of T12 bulbs varies from 15 inches all the way to 12 feet. They are available in two basic types: the standard and the high-output. Standard T12 bulbs have two pins on each end of the bulb. They provide a normal fluorescent light level for general applications. They should not be used in very cold areas, as they may fail to light up when temperatures get below 32. High Output T12 bulbs have one rectangular black plastic piece on each end of the bulb. The provide a higher level of light output than Standard T12 bulbs and use more wattage to do so. They are used in cold temperature locations, such as garages, outdoor signs, and freezers.
Please note - T12 tubes have now ceased production worldwide. We strongly advise stocking up on T12 tubes if you are not looking to change your light source in the short term..
2-Pin & 4-Pin
Compact fluorescent lamps (CFLs) are miniature versions of full-sized fluorescents that give off light that is similar to common incandescent bulbs rather than the fluorescent tunes used factories and schools. Current UK building regulations require a proportion of light fittings in newly built houses to be designed with 2- or 4-pin sockets, instead of the usual bayonet or screw fittings, so that they will only accept CFLs.
Bases & Sockets
The base of the CFL is the part that plugs into the electrical socket. Bases for CFLs are available in three forms: screw-in, 2-pin, and 4-pin.
- Screw-in base - Identical to those used for incandescent bulbs, making them ideal for replacing screw-fit incandescent bulbs.
- 2-pin base - Found on CFLs with pre-heat starting. Each 2-pin lamp has an integral starter and requires a separate ballast.
- 4-pin base - Used on CFLs with rapid or instant start. 4-pin lamps require a separate control gear and starting device.
Pin-base CFL lamps are obtainable in a wide selection of outputs and sizes, making them an attractive option for both end-users and specifiers. Bear in mind that CFLs should not be used with the standard domestic wall-mounted dimmer switch. It is possible, though, to dim 4-pin lamps with specialist control gear and a compatible dimming controller.