Introduction

Lighting represents a surprisingly large part of the electricity consumption of a typical house. We begin with a quick summary of the domestic lighting situation, emphasising the advantages and disadvantages of different types of low-energy lighting. More detailed information is given in the sections that follow.

Incandescent bulbs

The most common form of domestic lighting at present is incandescent bulbs, where light is generated by a very hot metal filament. It is a flexible source of lighting which is cheap to install but very inefficient and expensive to run. It is best used in places where light is only used occasionally and for short periods. Due to their inefficiency, incandescent bulbs are gradually being taken off the market, starting with the larger 100 and 150 watt sizes.

Halogen lamps

The popular halogen lamps are also filament bulbs, filled with a gas including a halogen such as iodine. They run at higher temperatures and so produce a whiter light. Halogen lamps are somewhat more efficient than ordinary incandescents but cost more. The main reason for choosing them is their intense white light from a very compact package – the efficiency benefits are minor, and they still waste most ot the energy as heat.

Fluorescent tubes

The light from fluorescents comes from a mercury plasma that produces ultraviolet light, which is converted to visible light by a fluorescent phosphor coating on the inside of the tube. The efficiency is typically four to five times better than incandescent lights, and fluorescent tubes last much longer than incandescent or halogen bulbs. For many years they have been used in kitchens, utility rooms and garages. There is now a variety of shapes in addition to the traditional long straight tubes, including smaller ceiling lights incorporating reflectors for higher efficiency and compact wall fittings.

Fluorescent lights need extra components, typically a starter to trigger them and a ballast to control the plasma. There are two general types of ballast – magnetic and electronic. Electronic ballast increases efficiency and avoids flicker and hum, as well as starting up instantly and not needing a starter. Some types of fluorescent fittings can be dimmed. The EU plans to phase out magnetic ballasts because of their disadvantages.

Compact fluorescent lamps (CFLs)

Now widely available, CFLs, which are often simply called low-energy bulbs, use small fluoresent tubes. Unlike other fluorescents, they are designed to work in light fittings also used for conventional bulbs. The ballast and starter are built into the bulb. They are far more efficient and long-lasting than incandescent bulbs, and so much cheaper over their lifetime. The drawbacks, gradually being overcome, are that they are dim for a short time after switching on, and most models do not work with dimmer switches. A real example of the potential cost and energy savings with CFLs is given below.

Fluorescent lighting, mainly CFLs, is currently the best option from the energy and cost point of view for domestic lighting which will be on for reasonable periods, unless there are good reasons why the slow switch-on time and lack of dimming are important.

Light-emitting diodes (LEDs)

LEDs are semiconductor devices that generate light when a low-voltage current is passed through them. Although each tiny diode is not very bright, large arrays are getting less expensive. They are excellent for battery-powered devices. Widely used as indicator lights and for text displays, brighter versions are now used in torches, traffic lights, and bicycle and car lights. They are potentially even more efficient than CFLs, come on instantly, can be dimmed, and have extremely long lifetimes. LEDs are slowly beginning to appear in domestic applications, but widespread usage awaits improvements in colour balance and ways of diffusing the very directional light. This could open interesting creative possibilities due to not needing bulbs or tubes.

High-intensity discharge lamps (HIDs)

Discharge lamps generate light by means of an electrical discharge giving off visible light. They are widely used in applications where a lot of light is needed over a very large area, such a street lights, because they are very efficient. However, they are very slow to start up, expensive, and do not provide good colour balance, so are not much used in normal domestic environments.
 

Summary of Main Features

Cost has been omitted as the prices of both CFLs and LEDs are coming down rapidly.

Incandescent Bulbs

Incandescent lighting is still the most popular form of lighting for homes. The light comes from a fine filament, normally of tungsten, which is heated electrically until it gives off visible light. The filament is usually in the centre of a glass bulb, evacuated to minimise heat loss through convection.

The filament evaporates at a rate strongly dependent on temperature, but higher temperatures give more visible light for the input energy. Thus there is a compromise between the life of the bulb and its efficiency. The normal compromise gives a life of about 1000 hours, though big power fluctuations can cause premature failure. Long-life bulbs last longer but give less light for the same electricity consumption. The light is a warm white, with more red than blue in the spectrum. Some lamps are filled with an inert gas such as argon. This allows a higher temperature for the same lamp life.

Efficiency

Incandescent lamps are inexpensive to buy. However, they radiate most energy in the infrared (i.e. as heat) and are inefficient for generating visible light, so they are expensive to run. Lower power lamps and torch bulbs are particularly inefficient. Because they are so inefficient they are gradually being removed from the market, starting with the larger 150 and 100 watt sizes.

The lamps start generating close to their full output in a fraction of a second after they are switched on. They can be dimmed easily by reducing the temperature of the filament, either by reducing the voltage across the lamp or by pulsing the current supplied. An incandescent lamp on mains electricity has a slight flicker at 100 Hz, but this is not noticeable as the filament does not cool much in this time.

Fittings and types

Two fittings for mains-driven incandescent lamps predominate in the UK, as shown in the pictures. Bayonet Cap (BC), fitting code B22d, is the most common. Edison Screw (ES), code E27, is less common in the UK but more widely used elsewhere. Other fittings include the Small Edison Screw (SES), code E14, and striplights of either 221mm or 284 mm length.

The main kinds of lamp are regular, candle, reflectors (spotlights) in various sizes, globes, and striplights. A regular bulb costs as little as 25p but other lamps can cost up to about £2.

End of life

Incandescent lamps consist of glass and metal. They do not contain any materials that will harm the environment, so they can be thrown away with household waste. They should not be placed in containers for recycled glass, however, because the glass used for these lamps is not the same as the glass used for bottles.

Conclusion

Although easy to use and cheap to buy, ordinary incandescent bulbs are the most inefficient and expensive source of domestic lighting. Their sale is gradually being banned.
 

Halogen Lamps

Halogen lamps are incandescent lamps in which the evaporation of the filament is reduced, giving a brighter light and a longer life. The bulb is filled with an inert gas containing a trace of a halogen such as iodine. The tungsten on the filament evaporates slowly and is deposited on the inner surface of the bulb. Provided that the surface is hot enough, the iodine reacts with the tungsten to make a gas, which is then broken down by the heat of the filament to redeposit the tungsten on the filament. The design lifetime is normally about 2000 hours. Halogen bulbs are usually made of quartz rather than glass, as this withstands the higher heat better. This very hot surface can be a safety concern.

Halogen lamps generate intense white light from quite small bulbs. They are used in outdoor floodlights and car headlights, as well as compact reading lamps and various low-voltage portable equipment. Some small bulbs include reflectors, and are very popular for providing multiple sources of bright, directed light in restaurants, kitchens, etc.

Ideally the bulb should not be touched directly, as grease from a finger on the quartz bulb can generate a hot spot which reduces the life of the lamp.

Efficiency

Halogen lamps provide up to twice as much visible light as a normal incandescent bulb of the same wattage, and as the filament is hotter the light spectrum is closer to daylight. Their greater efficiency and longer life makes their overall operating cost potentially cheaper than normal incandescent lights. However, the tendency is to use halogen lights with higher power than the incandescent lamps they might replace, which nullifies any energy saving. They are dearer than normal incandescents, with bulbs costing from about £3 upwards.

Halogen lights can be dimmed, but since the method of maintaining the filament depends on having a hot bulb they are not ideal for dimming.

Fittings and types

There is a huge variety of bulb types. Some operate at mains voltage, but even for normal domestic use many light fittings include transformers so that the bulbs operate at low voltage. This makes wiring easier and safer, but if the transformers are not switched off there is some wasted energy. Common types are small capsules or bulbs, and lights with reflectors (see pictures), as well as the small, thin tubes used in outdoor floodlights.

End of life

Halogen lamps contain very small quantities of halogens and halogen-hydrogen compounds, but the amounts are insignificant (only a few millionths of a gram). The lamps can therefore be thrown away with household waste. As they are made with quartz they cannot be recycled with glass.

Conclusion

Although more efficient than ordinary incandescent bulbs, halogen lamps are also unacceptably wasteful of energy and expensive to run compared to other light sources.
 

Fluorescent Tubes

A fluorescent tube generates light by creating a plasma in mercury vapour contained in a glass tube. The plasma generates ultraviolet radiation. The inside surface ot the tube is coated with a fluorescent phosphor which absorbs the ultraviolet and generates visible light. The colours generated depend on the phosphors used. Typically the light is concentrated on a few colours, for example yellow and blue, and the human eye interprets this as white. Fluorescents for general use typically produce one of several colour blends:

• Daylight – more blue, to seem like the outdoors.
• Cool white – the traditional colour often used in shops and offices.
• White – a bit more red in the mix, and the most commonly supplied with domestic fittings.
• Warm white – closest to the colour of incandescent lights, and probably the best for a home environment.

Because of the peaky spectrum of light generated, colours viewed under fluorescent light often differ from their colours in daylight – in particular reds can look darker.

In domestic use, many houses use fluorescent tubes in kitchens, utility rooms, garages and bathrooms. They are used much less often in living rooms, bedrooms, etc. as fluorescent light and fittings often seem colder and more 'industrial'.

Ultraviolet lamps omit the phosphor and transmit the ultraviolet radiation directly. They are used for disinfection chambers and sun beds. Black-light fluorescents convert the original ultraviolet light into the near ultraviolet, which can then generate strange theatrical effects when shined on paints and other materials which fluoresce in visible colours.

This section discusses the traditional fluoresent tubes that have been available for many years as well as some improved modern varieties, while compact fluorescent bulbs are treated separately in the next section. The important distinction is that compact fluorescent bulbs work in the same fittings as incandescents, while other fluorescents need dedicated fittings.

Efficiency

The main advantages of fluorescent lights over ordinary or halogen incandescent lamps are that they generate much more visible light for the same input energy, last much longer, and their surface is much cooler.

A rough rule is that they use only about a quarter as much energy as incandescents to produce the same amount of light. However, the light output depends on the colour balance – the cooler mixes tend to be more efficient than the redder ones, so for example a white tube will usually produce more light than a warm white one of the same wattage. However, there are slightly more expensive warm white variants (e.g. GE Polylux XLR) that do produce more light while also claiming improved liftetime. It is also worth noting that it can take a fluorescent a few moments to come up to full intensity, especially in a cold environment, and that the light output drops by about 20% over the life of the tube. The typical lifetime is usually stated to be about 10,000 hours, with some tubes claiming 15,000 hours, but this depends on how often the tube is switched on and off – sometimes a life of 50,000 on/off cycles is claimed.

Fittings and types

Fluorescents require extra equipment in addition to the tube. In older-style fittings a starter heats electrodes at each end and then opens the circuit. This triggers a spike of voltage to start the plasma, which often flickers on and off a few times before becoming continuous. A magnetic ballast (consisting of an inductor) assists in generating the initial spike, and then limits the current in the tube, which otherwise would become excessive after the plasma has been created. Such fittings sometimes flicker and hum in an irritating way at 100 Hz, especially as they age. The light can cause moving machinery to appear stationary.

Modern fittings are available that have electronic ballasts with no separate starter, and operating at higher frequency (e.g. 25 kHz). The light comes on instantly without flickering, and in operation annoying hum and flicker are less of a problem. Electronic ballasts can be designed to support dimming of fluorescents, keeping the filament hot while reducing the current across the tube. However for this to work there must be a good match between the dimming control and the tube. Some lights with integral ballast have been developed to provide dimming in conjunction with incandescent dimmers. The EU is planning to phase out the older type of fitting with magnetic ballasts.

Conventional fluorescent tubes come in a variety of lengths and diameters. The main diameters are:

• T2 – miniature, 7 mm diameter with lamps including one of 6 watt and only 219 mm long. Ideal for use in confined spaces, such as under wall units above kitchen worktops, in cupboards and wardrobes, etc. as they give off very little heat.
• T5 – 16 mm diameter.
• T8 – 25 mm diameter, used in most modern domestic fittings.
• T12 – 38 mm diameter, used in older domestic fittings.

There are also circular and U-shaped tubes in various sizes. In general, the longer the tube the higher the wattage and light output.

Sometimes low-energy bulbs with separate ballasts, rather than CFLs, are required by UK building regulations because this makes it difficult for the residents to introduce incandescent replacements. If a separate ballast is used in a pendant light, some designs of ballast have a larger ring to hold the lamp shade than the standard one used with incandescent lights. This can lead to difficulty in finding appropriate shades.

A standard fluorescent tube costs from about £3. For example, a 58-watt tube (often used in kitchens or utility rooms) might cost £5, with a warm white version offering more light output and longer lifetime for £6. More unusual designs can cost up to perhaps £15. The range of tubes and fittings in DIY or electrical shops tends to be quite limited, but a list of online suppliers is given below.

Recent developments

In recent years a number of more compact and efficient designs using different tube configurations have appeared. Sometimes confusingly called compact fluorescents, these differ from the low-energy bulbs (CFLs) described below because, like traditional fluorescents, they do not include a ballast in the tubes and so cannot be used in incandescent-type fittings. Some of these have four pins and others only two; the ones with two pins have built-in starters. See the bottom two pictures at right.

There are ceiling lights that use several parallel, shorter tubes in recessed reflector fittings that are designed to maximise light output to the room. These are mainly designed for public buildings and offices (typically with false ceilings) rather than domestic use.

However, some newer wall-mounted designs are quite acceptable for domestic living areas. These use fairly short tubes, sometimes bent to form an extended closed shape, as in the picture, and placed behind a glass or plastic diffuser. These fittings produce a lot of light and lie fairly flat on the wall; they are on sale in DIY and electrical shops.

End of life

Fluorescent tubes contain some mercury and so require special treatment, available at local waste disposal centres.

Conclusion

At the present time, fluorescent tubes are a very effective way to reduce both energy usage and costs. The main choice is between dedicated fluorescent fittings with a separate ballast, and more conventional fittings and lamps that require the use of compact fluorescent bulbs, discussed in the next section.
 

Compact Fluorescent Lamps (CFLs)

Compact fluorescent lamps are low-energy light bulbs that can be used as direct replacements for conventional bulbs. A CFL is built with an integral electronic ballast and starter, and typically has either a bayonet or Edison screw fitting so it can be powered by the same fittings as incandescent bulbs. This section concentrates on CFLs, often simply called low-energy bulbs – more conventional fluorescent tubes requiring fittings with separate ballasts are discussed in the previous section.

When CFLs were introduced they were too big and heavy for many existing light fittings, and cost £10 or more. They took quite some time to reach full brightness, and were usually dimmer than expected. Current models are far better, offering both the original straight-tube shapes and very compact spirals that fit into almost all light fittings. They are also much lighter in weight. Other shapes are also available, such as globes and candle lamps. CFLs that can be dimmed are now available but not yet common. CFLs are still a bit dim at turn-on, but brighten up fairly quickly. Costs have come down to the point where the most popular sizes can sometimes be found in multiple packs for less than £1 each. The situation is continuing to change rapidly, with improved versions appearing at a rapid pace.

However, CFLs are still noticeably dimmer in cold surroundings, and are not suitable for locations where they are only switched on for very short periods (e.g. a cupboard).

Efficiency

CFLs share the advantages of fluorescent tubes. Being built in a much more compact package does somewhat reduce the amount of light produced for a given amount of energy, but compared to incandescents the energy usage, running costs and lifetime are vastly improved – see the real-life example below. The energy saving is so large that they pay for themselves within a few months. And although one CFL costs more to buy than one conventional bulb, the far longer lifetime means that for cost comparisons buying one CFL should really be compared to buying about 10 incandescent bulbs.

Many people have noticed that the wattage equivalents claimed on CFL packaging tend to be a bit overstated. These usually suggest replacing an incandescent bulb by a CFL with a wattage rating of one-fifth or less, for example replacing a 60 watt bulb by an 11 watt CFL. This is often too dim, and discourages people from using CFLs. It is often better to go up to the next available rating, using a CFL with about one-quarter of the wattage rather than one-fifth – for example replacing a 60 watt incandesent bulb with a 15 watt CFL, or a 100 watt incandescent with about a 23–25 watt CFL.

Fittings and types

CFLs come in a wide and expanding variety of sizes and shapes, as shown in the pictures. However, if you want to put one into a constricted light fitting it sometimes takes a bit of care to obtain a CFL of the right wattage that fits in. The main styles currently available are: small U-tubes (two to four tubes), spiral, globe (like a conventional bulb), candle, and reflector. Many CFLs are Edison screw, and although some light fittings in the shops are also Edison screw, it is quite difficult to buy Edison screw replacement bulb sockets for fitting yourself.

The most common ratings range from 7–8 watts up to about 23–25 watts. Larger sizes and a full range of shapes are harder to find in shops. For example, to replace a 150 watt conventional bulb a 30 watt CFL is recommended. A list of online suppliers offering a far wider range of bulbs and fittings is given below.

Another advantage of CFLs is that they produce much less heat than the equivalent incandescent bulb, so that a higher-wattage CFL can be used in a fitting that can only handle a relatively low-wattage incandescent. However, for CFLs of more than about 20 watt it is still necessary to be sure there is adequate ventilation.

CFLs that can be used with conventional dimmer switches are still not common but they are becoming available. There are also CFLs with light sensors built into their bases, so that they can automatically turn on at night.

End of life

Compact fluorescent lamps contain a very small amount of mercury and so require special treatment, available at local waste disposal centres.

A real-life example

Most people who replace their bulbs with CFLs do so a few bulbs at a time, making it difficult to evaluate the energy and cost savings accurately. However, a member of the Energy Initiative Committee replaced virtually all of the incandescent bulbs in his house over a very short time, and carefully monitored the change in electricity bills. This was quite a clear case: the house already had fluorescent tubes in the kitchen, utility room and bathroom, with ordinary incandescents everywhere else. The incandescent bulbs ranged from 60 watts to 150 watts, and the two dozen or so replacement CFLs from 11 watts to 30 watts. Some 60 watt bulbs were replaced by 15 watt CFLs rather than the 11 watt ones recommended on the CFL packages in order to get adequate light.

Comparing electricity bills over a full year with bills from previous years, the energy consumed was reduced by about 1500 kilowatt-hours over the year. At current electricity prices that saves at least £180 per year. The cost of the CFLs was paid back within a couple of months. However (as noted above), if we compare the price of one CFL with the ten or so ordinary bulbs that would be needed over its much longer lifetime the CFL is probably cheaper to buy, even without taking the hugely reduced electricity consumption into account.

Conclusion

At the present time, compact fluorescent bulbs are a very effective way to reduce both energy usage and costs. The main choice is between dedicated fluorescent fittings with a separate ballast (discussed in the previous section), and more conventional fittings and lamps using compact fluorescent bulbs. For most domestic purposes, compact fluorescent bulbs are probably the best choice at present.

Light-Emitting Diodes (LEDs)

Passing current through special types of semiconductor diodes generates light. The colour generated depends on the materials making up the diode. For many years red, yellow and green LEDs have been used as indicator lights, or for simple alphabetic or numeric displays. LEDs can be shaped, for example to produce the widely used 7-segment numeric displays in digital clocks. The invention of blue and then ultraviolet LEDs led to the production of white LEDs. White-ish light is generated either by combining diodes of different materials, or by coating a diode which generates ultraviolet with a suitable phosphor. The operating voltage across the diode is about 1 volt, which means that battery operation is an attractive option. Another attractive feature is that they last far longer than ordinary lighting, with lifetimes claimed to be 50,000 hours or more. This makes them useful for reducing failures and maintenance, especially in safety-critical applications or in places that are difficult to access. For example, arrays of LEDs are now used for traffic lights, some car lights, etc.

LEDs come on at full intensity, and are very easy to dim. They would therefore overcome some of the objections to compact fluorescent bulbs.

Efficiency

The light emitted by one diode is not very bright, but several diodes can be combined to make a torch or bicycle light that is more compact and uses much less battery power than an incandescent bulb. Arrays of many diodes are fabricated using some of the same large-scale production techniques used for electronics. The light is emitted directionally, but that is a useful feature for many of the current applications (e.g. torches).

The efficiency of the brightest LEDs been increasing steadily. Even at efficiencies comparable to incandescents they have the advantages of low-voltage operation and long life, and are therefore in widespread use as indicators, illumination signs, and more recently torches.

LED lighting is under very active development. Efficiency is now comparable to fluorescents and at the same time costs are coming down. To be useful in domestic surroundings the colour balance of white LEDs needs to be improved, but already some specialised domestic LED lighting is available in the shops.

The future of LED lighting has great potential. Producers predict that efficiencies two or three times better than fluorescent lights seem possible. If this is combined with acceptable colour balance, and a way to produce diffused light to fill a room, there is a possibility of a true revolution in lighting since arrays of LEDs need not come in the form of bulky bulbs or tubes. Rooms might be lit by large-area flat panels or interesting shapes.

End of life

Light-emitting diode lights would generally be classified with other electronic goods, and should be brought to local waste disposal centres. As they are not yet in common use it is not entirely clear what the recycling situation is.

Conclusion

Light-emitting diodes are potentially even more efficient than CFLs, but more development is needed before they can be regarded as a solution for general domestic lighting.

High-Intensity Discharge Lighting (HID)

The technology of these lamps is somewhat similar to that of fluorescents. A discharge is created in a tube, but in discharge lighting the light is produced directly in the visible range rather than ultraviolet. As a result even higher efficiencies, up to 150 lumens per watt, can be achieved. To reach the rated light output it is normally necessary to evaporate a metal in the tube, so that the lights can take about 15–30 seconds to reach full brightness, and may need to be off for 30 seconds before they will re-light. Discharge lighting is therefore normally used in environments where bright lighting over a wide area is required for long periods, for example in sports halls, warehouses, street lighting, agriculture, and indoor gardening. They have also been used, with some controversy over their brightness and colour, for vehicle headlights.

The discharge is triggered between tungsten filaments along a quartz or alumina tube. The most common technologies at present are metal halide (picture) and high-pressure sodium, both of which give a white-ish light. Low-pressure sodium, widely used in street lights, is the most efficient of the lamps, but produces an almost purely yellow light which makes recognising colours impossible. The earliest lamps used mercury vapour, which gave a blue-ish light including considerable ultraviolet, which had to be filtered out.

A high-intensity discharge lamp typically costs around £30 and lasts between 5000 and 20,000 hours.

End of life

Most discharge lamps contain some hazardous materials and so require special treatment, available at local waste disposal centres.

Conclusion

Although very efficient, discharge lamps have too many drawbacks for general use in domestic lighting.
 

Low-energy Lamp Suppliers

Manufacturers

These are some of the main companies producing low-energy lamps, with links to their websites:

Crompton
GE Lighting
Megaman
Osram
Philips Lighting
Sylvania

Suppliers

Common styles and sizes of CFLs and fluorescent tubes can be obtained from supermarkets, electrical, and DIY stores. There are sometimes special deals, especially on packs of several CFL bulbs. However, the choice tends to be quite limited. A wide range of lamps can be bought or ordered from Didcot Electrical Wholesalers, 66–68 Broadway, Didcot OX11 8AE (01235-819181). Internet sources can be less expensive, particularly if buying in any quantity, and offer a very full range if you look around. Some useful suppliers are:

BLT Direct
Commercial Lamps
Energy Bulbs
GB Bulbs
The Greenshop
Jersey Lightbulbs
The Light Bulb Company 74–77 Magdalen Road, Oxford OX4 1RE, 01865-794500
Live and Neutral
Maplin
Netlamps
Next Day Lighting
Ultima Store
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