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4.2.1 Lamp types

Although traditional incandescent electric light bulbs (also known as ‘General Lighting Service’ or GLS lamps) have been sold by wattage as ‘60 watt’ or ‘100 watt’ lamps, what actually counts is the amount of light they produce. This is measured in units of lumens (lm). For example a 100 watt GLS lamp produces about 1200 lumens. Modern lamp packaging now clearly states the light output allowing a clear comparison between the wide range of lamp technologies now on sale.

Table 12 gives a brief summary of different types of lamps. The sale of conventional incandescent and many types of halogen lamps is now being phased out almost worldwide, since they can be conveniently replaced with lower energy LED and compact fluorescent alternatives.

Table 12 Descriptions of lamp types
Lamp type Details
General lighting service (GLS) The traditional incandescent light bulb
Tungsten halogen

Miniature incandescent lamps. Substitutes for conventional GLS lamps use minature halogen bulbs inside a GLS-sized casing
Fluorescent high-pressure mercury discharge lamp (MBF) Bluish white light, often used for shop lighting
Metal halide high-pressure mercury discharge lamp (MBIF) Bluish white light, used for street lighting
Compact fluorescent lamp (CFL) Replacement for normal incandescent light bulbs
Tri-phosphor tubular fluorescent Standard type for office and shop lighting
High-pressure sodium discharge lamp (SON) Orange-white light, used for street lighting
Low-pressure sodium discharge lamp (SOX) and higher-efficacy version (SOX-E) Pure orange light, used for street lighting
Light-emitting diode (LED)

Available in white and a range of colours

Replacement for normal incandescent light bulbs and now widely used for street lighting

An important factor in choosing a lamp is its luminous efficacy , the amount of light emitted in lumens per watt of electricity used (lumens W-1). This figure is also likely to be found on modern lamp packaging. Another important factor is the colour rendering index (CRI), which measures how well the light from a lamp imitates the broad spectrum of white light from the sun. GLS and tungsten halogen lamps have very good colour rendering while that from orange sodium street lamps is very poor.

Figure 42 shows the efficacies of the different lamp types listed in Table 12 and how, for a given type, the efficacy increases with power.

Described image
Figure 42 The efficacies of various lamps (adapted from Beggs, 2002) and manufacturers' literature
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This is a line chart showing the performance of different lamp types of different power ratings. Generally for any given lamp type the efficacy increases with power rating and light output. The x-axis is labelled ‘initial lamp lumens’. It has a logarithmic scale running from 100 lumens at the left to 100 thousand lumens at the right. The y-axis is labelled ‘luminous efficacy in lumens per watt’ and has a scale running from zero to 200. A black line representing the performance of conventional incandescent general lighting service or ‘G’’L’’S’ lamps appears at the bottom of the chart. At the left hand end is a lamp with a 15 watt power rating. This has a light output of about 120 lumens and an efficacy of about 8 lumens per watt. At the right hand end of the line is a lamp rated at 1000 watts. This has a light output of 2000 lumens and an efficacy of 20 lumens per watt. Above this is another black line labelled ‘tungsten halogen’. At the left hand end is a lamp rated at 100 watts. This has a light output of about 1500 lumens and an efficacy of about 15 lumens per watt. At the right hand end is a lamp rated at 2000 watts with a light output of 4000 lumens and an efficacy of 20 lumens per watt. Above this to the left is another black line labelled ‘’C’’F’’L’ or compact fluorescent’. At the left hand end of this is a lamp rated at 5 watts. This has a light output of about 220 lumens and an efficacy of about 43 lumens per watt. At the right hand end of the line is a lamp rated at 23 watts. This has a light output of 1400 lumens and an efficacy of 60 lumens per watt. To the left of this line is a white area in the chart labelled ‘white light emitting diodes’. Two arrows show the progressive development from about 100 lumens output at an efficacy of 40 lumens per watt towards 500 lumens output at an efficacy of 80 lumens per watt. In the centre right of the diagram is a green line labelled ‘’M’’B’’F’ or high pressure mercury discharge lamps’. At the left hand end is a lamp rated at 50 watts with a light output of 2000 lumens and an efficacy of 40 lumens per watt. At the right hand end is a lamp rated at 1000 watts with a light output of 6000 lumens and an efficacy of 60 lumens per watt. In the centre of the diagram is a black line labelled ‘fluorescent (tri-phosphor)’. At the left hand end of this line is a lamp rated at 18 watts with a light output of 1400 lumens and an efficacy of 80 lumens per watt. At the right hand end of the line is a lamp rated at 100 watts with a light output of 95000 lumens and an efficacy of 95 lumens per watt. To the right of this line is another one coloured orange labelled ‘’S’’O’’N’ or high pressure sodium discharge lamps’. At the left hand end of the line is a lamp rated at 50 watts with a light output of 3800 lumens and an efficacy of 75 lumens per watt. At the right hand end of the line is a lamp rated at 1000 watts with an output of 120 thousand lumens and an efficacy of 120 lumens per watt. Beneath this line at the right of the diagram is a green one labelled ‘’M’’B’’I’’F’ or metal halide high pressure mercury lamps’. At the left hand end of this line is a lamp rated at 250 watts with a light output of 20 thousand lumens and an efficacy of 80 lumens per watt. At the right hand end of the line is a lamp rated at 1000 watts with a light output of 9500 lumens and an efficacy of 95 lumens per watt. At the top right of the diagram is an orange line labelled ‘‘S’’O’’X’ or low pressure sodium discharge lamp’. At the left hand end of this line is a lamp rated at 35 watts with a light output of 4500 lumens and an efficacy of 130 lumens per watt. At the right hand end of the line is a lamp rated at 180 watts with an output of 35000 lumens and an efficacy of 190 lumens per watt. Above this line and to the left is another orange line labelled ‘’S’’O’’X’’E’ or higher efficacy low pressure sodium discharge lamp’. At the left hand end of this line is a lamp rated at 18 watts with a light output of 1800 lumens and an efficacy of 100 lumens per watt. At the right hand end of the line is a lamp rated at 131 watts with a light output of 26000 lumens and an efficacy of 200 lumens per watt.

Figure 42 The efficacies of various lamps (adapted from Beggs, 2002) and manufacturers' literature

Very high efficacies are available for street lighting, but most domestic applications require lamps of under 1000 lumens output. Until the appearance of CFLs in the 1980s there were no high-efficacy low-powered lamps, yet this is where most domestic lighting applications lie. There was a large gap at the left side of Figure 42 that needed filling by new technologies. For domestic use the ‘standard’ light bulb (for over 70 years) has been the 800 lumen 60 watt GLS incandescent lamp. Its attractions were its familiarity and its good colour rendering, yet it only had an efficacy of 13 lumens W−1.

Its rivals, the compact fluorescent lamp (CFL) and new white LED lamps are considerably more efficient and have a longer life expectancy but do not have the same quality of colour rendering. LED lamps give full brightness when switched on unlike CFLs which may take several minutes to warm up. The sale of conventional GLS incandescent lamps has largely been phased out in Europe and many other countries as an energy efficiency measure. Small halogen incandescent lamps remain on sale. These are 30% more efficient than GLS lamps and have a good colour rendering index. However the sale of even these is currently (2023) being phased out, since they can be replaced with LEDs.