Building services: lighting types in commercial use
Green lights
10 January 2011
In his second article on lighting, Simon Dove looks at the other main lamp types in commercial use today: incandescent lamps and discharge lamps, including fluorescent
As with LEDs, the issues influencing lamp choice include energy efficiency, quality of light and cost. To appreciate the rationale behind the selection it is essential for surveyors to understand the design and what is needed to create a well-lit environment.
Incandescent
Also known as tungsten (due to their tungsten filament) these have existed for many years – the basic tungsten, the general lighting service lamp (GLS, or the household ‘bulb’) has changed little since Thomas Edison developed this technology in the 1870s. However, with a relatively short lamp life and low luminous efficacy, its energy inefficiency is now hastening its decline. A 2009 European Union Directive began the phasing out of GLS lamps. This started with the highest wattage lamps (more than 100W) and will gradually cover lower wattages. It is anticipated that the final phase out will be complete in 2016.
Options available
A variety of tungsten sources are available – used in everything from domestic, leisure, theatrical and medical applications – and the efficiency of lamps can vary greatly. A variation of the basic GLS lamp is the tungsten halogen (TH). TH is smaller, more efficient, has a longer life and also gives a whiter light than GLS. TH has a higher efficacy (lumens/Watt) over conventional incandescent lamps. The lamps are either 230V or operate on 12V, in which case they require an electronic transformer.
Current/emerging technology
The GLS lamp is popular in the home and people like the warm white light generated. Current energy efficient alternatives are based around a compact fluorescent source but there is a general dislike of these lamps, with the perception that they offer a cold, flat alternative (hence the reports of people stocking up on GLS lamps while they are still available). TH is still being developed. There are new lamps on the market, similar in shape to the conventional GLS lamp but with a tungsten halogen burner. These can be inserted in to a standard lamp holder, are easy to dim and produce a quality of light similar to the traditional incandescent.
One recent development of TH is the use of an infrared coating on the burner; this allows up to 30% more energy savings when compared with standard low-voltage GLS lamps. However, in the long-term, it is likely that the development of TH will be overshadowed by more energy efficient sources, such as the compact fluorescent and LEDs.
Pros and cons
GLS can offer a good quality of light. Its main disadvantages are its low efficacy (lumens per watt) and short lamp life.
TH has a number of advantages. It is small, is easy to control, can be dimmed down to 1% and can give instant light. Lamps are usually easy to replace and are readily available. TH offers excellent colour rendering and has been a popular light source for museums, galleries and retail environments where this is critical. With UV filters, TH can also deliver a light output with little or none of the pigment-damaging UV light. However, recent tests in museums and galleries have shown that high quality LED products are now becoming a viable alternative. Alternative sources, such as HID (see below), LED and compact fluorescent are also now becoming the standard in retail environments. Though better than GLS, TH also has low efficacy and a short lamp life.
Costs and lifespans
The GLS lamp can offer a life of approximately 1,000 hours and usually costs less than £1. TH typically gives around 2-4,000 hours and, with an average price of £2-3, is also inexpensive.
Planning issues
GLS and TH are generally used in domestic environments or in spaces where a lighting effect and low illuminance levels are required. Layout issues do not generally arise, although the TH 12V needs a transformer and so requires additional space.
What can go wrong?
Incandescent sources have been in existence for a long time; other than the problems associated with energy efficiency outlined above (and provided the lamps are purchased from a reliable, reputable source) there are unlikely to be technical problems.
The fluorescent lamp
The first viable fluorescent lamp came onto the market in the 1930s. It soon became widely used and had a significant effect on building design, e.g. it allowed for the design of deep plan offices as it replaced daylight as the main source of light. The fluore scent lamp is a low pressure discharge lamp and is generally regarded as sustainable.
Options available
Fluorescent lamps come in linear or compact forms and in a variety of shapes, sizes, wattages, colour temperatures and colour renderings. Both compact and linear forms have been used extensively in office and retail environments because of their low energy use and low maintenance. However, they have not been used extensively in homes because the quality of light is unpopular (unlike tungsten) and the domestic version was always hard to dim, although this is now changing.
Current/emerging technology
To start and run the lamp, control gear is required – this is now usually a high frequency (HF) ballast. Some of the latest HF ballasts have their own digital code so they can be addressed from a building management system, allowing lighting to be controlled and energy use minimised. Feedback can also be obtained from the luminaire indicating its condition. The fluorescent lamp is an easy light source to control and, within commercial applications, dimming is commonplace with daylight linking on the increase, whereby control technology enables lamps to be dimmed or extinguished when there is enough daylight for the given task to be undertaken. It should be noted that dimming ballast control technology for fluorescents must be specified at the outset because compatibility problems can occur if different control systems (such as digital and analogue) are used.
Pros and cons
Fluorescent lamps have a high luminous efficacy and even in the compact form perform well, with T5 lamps able to give an efficacy of 100 lumens/Watt. Traditionally, fluorescents have not had a good reputation for the quality of white light created. However, this has improved a lot recently and they now offer a range of good quality white light with colour temperatures ranging from 2,700K to 15,000K.
With the large choice of colour temperatures available, the selection of lamps can become an integral part of the design process. However, incorrect specification can lead to an inappropriate feel to the space: for example, the specification of cool colour temperature lamps can create a cold, stark environment.
The Colour Rendering Index (CRI) of a fluorescent lamp is generally above 80 and improvements have led to the introduction of lamps with a CRI of more than 90. The CRI uses a scale from 0 to 100, with 80-90 considered ‘good’ and anything above 90 ‘accurate’. Fluorescent lamps can therefore be used in environments that require accurate colour discrimination, such as medical areas and print rooms.
Fluorescent lamps do not give instant light as they take a couple of seconds to start up and gradually reach full output after a minute or two. Some, e.g. the T5, can experience difficulty in starting and reaching full output in cold environments. This could be problematic in the UK winter and should be considered when specifying for exterior use, such as in car parks.
Planning issues
The wide range of shapes and outputs allows fluorescents to be used in most environments. As efficiency has increased, so the size of fluorescents has decreased with T12 becoming T8 and now T5, which is just 5/8 of an inch or 16mm in diameter. Linear fluorescents generally have a higher light output and tend to be more ‘workaday’ and so are often specified for environments such as offices. Compact fluorescents can also be used but, generally, these are used in smaller, more decorative fittings where the emphasis is less on light output.
One of the vagaries of the T5 lamp is that it is available in two variants: high efficiency (1200mm, 28W) and high output (1200mm, 54W). These do not run on the same control gear and so care must be taken when relamping, e.g. if a high output lamp is installed within a high efficiency fitting then failures can occur. Lamps are constantly being improved and there is now a replacement for the T5 lamp which uses the same ballast but is, for example, 25W rather than 28W but with the same output. This could result in a significant energy saving in a large office development.
Costs and life spans
The price of fluorescents is low, typically starting at £2 depending on the supplier and the deals available – they are therefore considered an economical option. They are also cost-effective to run when taking into account their high efficacy (see Figure 1).
Figure 1: The efficacy of lighting options (© Hoare Lea)
Fluorescent lamp life is increasing, with some T5 lamps offering 40,000 hours as standard and 60,000 hours now available with longer life ballasts. This means less re-lamping and reduced maintenance.
What can go wrong?
The fragile nature of the fitting means it can be broken quite easily and the internal elements exposed. Fluorescents also contain a degree of mercury so care must be taken, especially in domestic settings.
Because fluorescent lamps have been around for a long time many problems have been ironed out. Installers are familiar with these lamps and can install them with relative ease. They are also easily replaced when a fault occurs. A bulk replacement would normally take place every two to three years, with spot replacement taking care of any individual failing lamps.
High pressure/high intensity discharge (HID) lamps
HID lamps have a strong place in the market. They were originally developed for exterior use and their high efficiency and lamp life made them ideal for lighting roads and sports stadiums, with lamps of up to 2,000W used to floodlight the latter. Their high luminous efficacy and low maintenance, together with a reduction in their size, means they are now also used in interiors with high ceilings or in uplighting luminaires, e.g. in secondary reflector systems. Here, luminaires are aimed at a large mirror which reflects the light. Secondary reflector systems are usually used in areas where maintenance would be difficult, for example an atrium.
Options available
Many options are available within this category of lamp family, in terms of wattages, outputs and colour temperatures. There are two basic types: mercury-based, such as metal halide, which have a cool, whiter colour appearance and sodium-based, which tend to have a warm, golden appearance. All discharge lamps require control gear. Some lamps with the same wattage can have a different lamp base and envelope shape so care needs to be taken when specifying and replacing lamps.
Current/emerging technology
Improvements in the colour rendering of HID lamps, together with their small size, have also led to their use within retail environments, where they are replacing TH.
Dimmable ballasts are still an emerging technology. Dimming has always been hard to achieve to a good standard. Generally, a reduction of approximately 50% is possible although this limits its flexibility. An area where dimming is becoming viable is in road and street lighting. Many local authorities are now employing sophisticated control systems which can provide feedback from the luminaires and allow dimming control over the lighting. Once switched off, HID lamps require up to 10 minutes to cool before being re-ignited, though development in ‘hot restrike’ technology is improving. HID lamps also require a run-up time of approximately three-four minutes.
Pros and cons
HID lamps have a very good light output, with some lamps in excess of 100 lumens/W. These lamps have a significant start-up time (they can take up to five minutes to reach full light output) which, in addition to the impractical warm-up times, the difficulties associated with dimming and the unnecessary intensity of light generated, makes them unsuitable for domestic settings. Metal halide lamps produce good white light and a variety of colour temperatures. Colour rendering is good with metal halide providing the best CRI within the 90+ region.
Costs and lifespans
Lamp life is generally good – in excess of 10,000 hours – but they are expensive at between £20-30.
Planning issues
HID lamps are getting smaller and can offer precise control and flexibility of design, e.g. their use on narrow or very wide beams. Planning and layout issues are minimal.
What can go wrong?
No major issues – HID lamps are reliable and robust.
A good scheme
Most schemes employ a mixture of lamp types, with the designer selecting the most appropriate source for the function and design aesthetic required. All of the lamps discussed have to be housed within an enclosure of some kind and the design and quality of this will impact on the final lumen output and the light output ratio. The enclosure will generally also contain any necessary control gear to provide electrical control for the lamp. Both lamps and their enclosures must therefore be carefully considered early in the design process. This is essential as many guidance documents purely concentrate on the efficiency (efficacy) of the lamp rather than the quality of the luminaire or the design philosophy behind its location within an interior. Lamps are undoubtedly important – but a good lighting scheme is more than just a lamp.
Simon Dove is an Associate with Hoare Lea Lighting
Further information
See also the related feature LED there be light.