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The professional term for what most of us call a light bulb is a 'lamp'. A lamp is simply an artificial source of light. There are hundreds of types that differ from each other in the way they generate light, how much light they produce, the power they consume and their efficiency. They also differ in respect to their shape, the type of light they produce and their beam characteristics.

I know that most of you will simply pop down the DIY centre and buy a light fitting and lamp to do the job and by and large that’s all you probably need to do, but it’s well worth considering some of the facts about different lamps and light fittings before the shopping trip as a little knowledge may help you buy the right lamp and save you a lot of money in the long term.

As I write this part, lamp manufacturers are starting to put lots more information about their lamps onto the packaging.  They are also putting additional information on their websites. Take a look at the table below to see what I mean. 

Information on lamp packaging



Nominal luminous flux (Lumens per Watt)


Will also show comparison between energy saving lamp and incandescent lamp

820 Lumens


15W Energy saving, equivalent to 65W incandescent bulb (The term energy saving can only be used for ‘A’ rated lamps)  


10yr – 10,000hr Lifespan if used for 1,000 hours per year  

Number of switching cycles

 Ëƒ10,000 on/off cycles  

Colour temperature

2700K = warm light  

Warm up time

60 sec to 60% of the full light output  

Warning if lamp cannot be dimmed or only on specific dimmers

DO NOT use with dimmer or electronic switches (photoelectric cells, timing devices)  

Information if the lamp cannot be used under standard conditions

DO NOT use below 0°C  

Lamp dimensions

L: 128mm W: 64mm  

Mercury content of mercury containing lamps

Bulb mercury content 3.0mg  

Website address in case of lamp breakage

For bulb breakage and end of life information see instruction leaflet enclosed and www


Lamp characteristics


This term describes the efficiency of a lamp at converting electricity into visible light.  The amount of light produced for each Watt of energy used is called a ‘Lumen’ and therefore the higher the Lumens per Watt the more efficient the lamp.  So look out for the amount of Lumens produced on the box labelling, as well as the wattage. 

If you mix in odd circles as I do you may occasionally hear people talking about the amount of ‘Lux’.  Lux is an abbreviation of ‘lumens per square metre’.  The greater the area that you want to light to a specific level of ‘lux’, the more lumens it will take.  For example, 1000 lumens will light one square metre to 1000 lux.  Using the same number of lumens to light 10 square metres will give you only 100 lux per metre.  Of course, it isn’t as straightforward as that, because the light doesn’t get evenly distributed over the full area in equal measure.  If you live in a big property and need to light the driveway and forecourt using lamp columns, for example, the lighting engineer will work all this out for you as she’ll know the light patterns produced by the various luminaires.

Colour Rendering Index (Ra)  

This term describes the quality of the light.  The higher the figure, the more accurately different coloured surfaces appear.  Most compact fluorescent lamps are classified as excellent (Ra 90 – 100) or good (Ra 80 – 89).  This information might be shown on the box, but if not will be shown on the manufacturer’s website.

Colour temperature

Measured in degrees Kelvin, the temperature of a lamp indicates how ‘warm’ the light is; the lower the temperature the ‘warmer’ the light.  The majority of compact fluorescent lamps are 2,700K, which can be considered as ‘warm’ light.  You may want a ‘colder’ light to illuminate the garden or the side alley, in which case you’ll need a lamp with a temperature of around 4,000K. This information will be shown on the box.

Lamp life  

Obviously this tells us how many hours the lamp will operate for.  Lamp life expectancy can be affected by the amount of switching, the quality of the luminaire it is contained in, the ambient temperature it operates in and its location.  The expected lamp life will be shown on the box.  If they last much longer the government may consider raising the retirement age for lamps (that was a joke).

Energy rating  

Rated in categories from A to G this familiar diagram on packaging has applied to lamps for some years.  Compact fluorescent energy saving lamps are category A.

Tungsten lamps

You will no doubt be aware that most of the traditional tungsten (incandescent) light bulbs are no longer on sale.  We have now lost the 40W, 60W, 75W and 100W ‘A’ shaped lamps plus the 60W golf ball shaped and candle shaped lamps.  There is no doubt that any remaining incandescent lamps will be withdrawn once the lighting industry has developed suitable low energy replacements, which are mainly compact fluorescent and LED lamps.  When you look at the table below you can see why this has happened. 

Tungsten Halogen

A tungsten halogen lamp is an incandescent lamp with a tungsten filament contained within a small glass bulb containing an inert gas and a small quantity of halogen gas.  These lamps produce excellent colour rendering and are generally more efficient than the ordinary tungsten light bulb. They are used extensively in domestic external floodlights, but are now available as replacements for the familiar tungsten light bulbs you used to be able to buy.  However, most are only rated C for energy, so you’re not going to save that much on your electricity bill. Also their lifespan is only a little longer than a tungsten light bulb.  But, most are dimmable (look at the packaging before you buy) and can often be used in light fittings that won’t take a CFL.

Compact fluorescent (CFL)

A compact fluorescent lamp, which some of you may call an energy saving bulb, is basically a fluorescent tube that’s been coiled up or shaped in some way to take up less space.  In recent years CFLs have been produced in sizes that enable them to replace the familiar tungsten light bulbs.

A replacement compact fluorescent lamp produces as much light as its tungsten equivalent, but does it using a lot less energy.  The lamp also lasts a great deal longer and nowadays there’s little difference in the quality of the light you get from the ‘warm light’ version.  They are more expensive to buy than tungsten light bulbs, but the extra cost is quickly recouped because of their efficiency.

Light emitting diodes (LEDs)

LEDs are the new boys on the block.  They are very small semiconductor devices that convert electricity into light using the movement of electrons.  Depending on the materials used to make it and the electric current running through it the light emitted can be of any colour in the visible spectrum and ultraviolet and infrared in the non-visible spectrum.  LED types include miniature, high-powered and multicoloured. High powered LEDs are formed into clusters to produce a variety of lamps that can replace incandescent and compact fluorescent lamps. They are very efficient and have a very long lifetime.  They’re also solid state and can (allegedly) be kicked around without breaking!  They’re being used in street lamps and in solar powered lamps and slowly they’re finding their way into people’s homes - I’ve got some in my kitchen and the bathroom mirror!  

Comparison of efficacy, colour and lamp life between different lamps

This table compares different light sources and gives approximate values for Efficacy, the quality of the light expressed using the Colour Rendering Index (Ra) and the expected lifetime for the lamp.  You will notice that as the efficacy improves you lose a little on the quality of the light, but gain a great deal on the lamp life.  If you do the sums you will save a huge amount on your electricity usage by switching to compact fluorescent and LEDs.



Lumens per Watt




Wax Candle



Depends on length!

60W Tungsten light bulb (now withdrawn from sale)




150W Tungsten halogen

10 - 30


2000 – 4000

Compact fluorescent

65 – 75

70 – 90

10000 – 15000

Light emitting diode (LED)

70 – 95

70 – 90

35000 – 50000

Fluorescent tube


65 – 90

10000 – 25000

High pressure sodium street lamp

90 – 150


16000 – 24000

Source:  Various sources were used to prepare this table.  Large variations were found between sources and therefore values should be treated as estimates only. On average the UK has 3,900 hours of darkness each year