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Incandescent Lamp
How it works
Incandescent Lamps are commonly referred to as ‘Light bulbs’. Light bulbs have a very simple structure. At the base, they have two metal contacts, which connect to an electricalcircuit. The metal contacts are attached to two stiff wires, which are attached to a thin metal filament. The filament sits in the middle of the bulb, held up by a glass mount. The wires and the filament are housed in a glass bulb, which is filled with an inert gas, such as argon.
When the bulb is connected to a power supply, an electric current flows from one contact to the other, through the wires and the filament. The filament is made of a long, incredibly thin length of tungsten metal. In a typical 60-watt bulb, the tungsten filament is about 2 meters long but only 0.25mm thick. The tungsten is arranged in a double coil in order to fit it all in a small space. In a 60-watt bulb, the coil is less than 25mm long.
As incandescent lamps have been in the market for over a century and originated as the main light source for domestic dwellings, many different types and sizes are available. See Below. The most common shape would be the ‘GLS’ or ‘General Service Lamp’ which would typically be found in pendants, standard lamps or table lamps. The next most popular lamp is the ‘candle’ shape which as the name suggests, effectively replaced the candle wall fixtures of the 19th century.
However, there are many other types such as ‘Globe’, ‘Reflector’, ‘Tubular’ etc. Reflector lamps (either blown bulb or PAR) are similar to GLS lamps but have a bulb with an internal reflector coating. Replacements should normally be of the same type as originally used unless it is desired to change the beam intensity and width. Crown-silvered lamps are intended to be used in conjunction with a metal reflector as part of the luminaire.
With the pressure to reduce energy consumption, the last 5 years has seen the consumer shift across from purchasing incandescent lamps to their replacement, Compact Fluorescent Lamps. More...
Incandescent lamps tend to be measured in terms of their power output or wattage. Over the years, the GLS lamp has reduced in size from 65mm diameter to 60mm to its current 50mm. Many of these shapes have a designation consisting of one or more letters followed by one or more numbers. The letters represent the shape of the bulb, numbers represent the maximum diameter, in millimeters e.g. A55 or in eights of an inch or PAR16 (i.e. 2”).
Lamp Base
As Incandescent lamps have been in the market for over 150 years, there are numerous bases available to suit every application. See appendix…
Incandescent lamps offer a low efficacy as the majority of energy consumed is converted into heat. A typical range would be 8-14 lm/w. The following table details the typical efficacies of the most common incandescent lamps.
Energy Rating
Even though they produce a high quality light, Incandescent lamps are the least efficient light sources. Typical energy ratings for incandescent lamps would be ‘E, F or G’ i.e. not very efficient. Under the EuP Directive, between 2009 and 2016, the majority of traditional incandescent lamps for general lighting purposes will cease to be sold in the UK.
The life of an incandescent lamp will typically last between 400 and 2,000 hours, dependent on the quality of the components used. End of life would be determined by the life of the filament. Failure can often be due to shock or vibration, which the lamp has sustained during transit, installation or use.
Also, during usage, the filament evaporates forming a black coating on the inside of the glass until eventually the filament thins and breaks. Some suppliers offer extended life GLS lamps e.g. 16 times normal life is claimed. These lamps are approximately half the efficacy of standard-life GLS lamps, which means they give only half the light output for the same power consumption.
Incandscent lamps start up instantly and achieve full brightness within less than one second.
One of the advantages of incandescent lamps is that they can be dimmed, utilising a standard Analogue (rotary) or DorS (digital) dimmer.
Incandescent lamps commonly operate directly on mains voltage, 220v – 250v AC, although many other voltages are offered. Incandescent lamps are very sensitive to changes in voltage.
For example, a supply voltage 5% higher than normal reduces lamp life by 60% but increases light output by 20%, whereas a supply voltage 5% lower would increase lamp life by 100% but reduce light output by 20%.
Colour Temperature
A typical incandescent lamp would produce a colour in the range 2,500 – 2,700 Kelvin. Incandescent lamps are recognized as producing a cosy, warm white light.
Colour Rendering
An incandescent lamp offers high colour rendering (100 on the CRI scale) i.e. it helps objects and persons illuminated to appear truer to life.
There are many different variations of finish available. Standard Incandescent finishes would be:-
  • Clear
  • Pearl
  • Pastel Colours
Consumers would tend to choose a particular finish to suit the application within their dwelling i.e. with an open shade, a ‘pearl’ finish would provide less glare than a ‘clear’ type. 
Filament lamps are mainly used for domestic and display lighting.
Low cost, simple operation, good colour rendering, dimmable.
Low efficacy and relatively short life.
Example of Range
The following table denotes the wide choice of shapes, sizes and colours in incandescent.
Key Properties

  • BS EN 60432-1: Safety specification for incandescent lamps. Tungsten filament lamps for domestic and similar general lighting purposes.
  • BS EN 60064: Tungsten filament lamps for domestic and similar general lighting purposes - Performance requirements
  • BS EN 50285: Energy efficiency of electric lamps for household use – Measurement Methods
  • BS EN 60630: Maximum lamp outlines for incandescent lamps
Halogen Lamps
How it works
A halogen lamp is an incandescent lamp in which a tungsten filament is sealed into a compact transparent envelope filled with an inert gas, plus a small amount of halogen such as iodine orbromine. The halogen cycle increases the lifetime of the bulb and prevents its darkening by re-depositing tungsten from the inside of the bulb back onto the filament.
The halogen lamp can operate its filament at a higher temperature than a standard gas filled lamp of similar power without loss of operating life. This gives it a higher efficacy (10-25 lm/W). It also gives light of a higher colour temperature compared to a non-halogen incandescent lamp.
Alternatively, it may be designed to have perhaps twice the life with the same or slightly higher efficacy. Because of their smaller size, halogen lamps can advantageously be used with optical systems that are more efficient.
Tungsten Halogen lamps have an increased light output and/or extended life compared with standard filament lamps. The bulb is of small dimensions, and made from quartz or hard glass. The most common halogen lamps tend to fall into 2 groups:-
Halogen lamps are available in a very broad range. No one will forget the mains voltage R7 halogen lamps for exterior floodlights.
One of the toughest decisions for the user to decide is which voltage. Original Halogen lamps were available in Low Voltage (12V) for use with a transformer to convert mains voltage into low voltage. 15 years ago, the GU10 Mains Voltage Halogen lamps were invented, negating the need for a transformer, thereby reducing cost, simplifying installation and maintenance. 
A reflector allows the user to direct light onto a particular surface or light an area or object. Typical beam angles would be 24 degrees or 38 degrees. A halogen lamp with a narrow beam angle is referred to as a ‘spot’ and a wide angle as a ‘flood’.
Dichroic or Aluminium Reflector
As well as producing excellent light output, a tungsten halogen lamp also produces a significant amount of heat. A dichroicreflector sends the majority of the heat backwards into the ceiling void or recess which is ideal for a ‘spot’ in an enclosed space. An aluminium reflector send the majority of the heat forwards which is ideal for enclosed light fittings, such as fire rated down-lights where the luminaire is completely enclosed.
The most common wattage is 50W. However, lower wattages are now being specified due to the need to reduce energy consumption. Some ‘Energy Saving’ halogen lamps can offer the equivalent light output matched with 20-30% energy saving.
Energy Savers
  • The technology used to achieve ‘Energy Saving’ versions depends on the voltage:-
  • Main Voltage Halogen lamps utilize a special gas fill to achieve a higher efficacy
  • Low Voltage Halogen lamps utilize an special Coating on the capsule which converts heat into visible light, hence Infra Red Coating (IRC)
  • Energy saving Halogen lamps are now available in the following types:-
  • Low Voltage Reflector and Capsule lamps
  • Mains Voltage Reflector (e.g. MR16) and Capsule lamps
  • GLS & Candle Look-a-Like Lamps to replace traditional incandescent lamps
  • Mains Voltage Linear Halogen lamps
Cap Type
Many different cap types exist. See Appendix…
High temperature filaments emit some energy in the UV region. Small amounts of other elements can be mixed into the quartz capsule, so that the doped quartz (or selective optical coating) blocks harmful UV radiation.
The efficacy depends on the voltage and whether energy saving version:
One of the main reasons for the use of halogens has been the ability to dim them. With legislation demanding more efficient lamps, halogen is being challenged by other light sources such as CFL and LED. However, with the advent of Energy Saving versions, halogen once more offers one of the best all round packages with its excellent colour rendering, bright light, improved efficacy coupled with dimmable capability.
Incandescent lamps start up instantly and achieve full brightness within less than one second.
Colour Rendering
An incandescent lamp offers high colour rendering (100 on the CRI scale) i.e. it helps objects and persons illuminated to appear truer to life.
Colour Temperature
A typical halogen lamp would produce a colour in the range 2,700 – 3,200 Kelvin i.e. a relatively comfortable, warm white light.
Low Voltage halogen lamps require a transformer to convert mains voltage into low voltage. Historically, halogen lamps have been linked up 2-4 lamps to 1 transformer. However, it is good practice to install 1 lamp to 1 transformer. More…
Halogen lamps are ideal for installation in the home, retail environments, studio in fact anywhere a bright, warm instant light is required.
Low cost, simple operation, excellent colour rendering, sparkle/bright light, dimmable. ‘Energy Saver’ halogen lamps meet the Energy Class ‘B’ or ‘C’ under the requirements of EuP Directive. Longer life verses standard incandescent.
Lower efficacy and relatively short life, compared to other lamps such as fluorescent.

Example of Range
The following table denotes the wide choice of shapes, sizes and colours in halogen.

  • BS EN 60432-2:2000: Incandescent lamps. Safety specifications. Tungsten halogen lamps for domestic and similar general lighting purposes
  • BS EN 60432-3:2003: Incandescent lamps. Safety specifications. Tungsten-halogen lamps (non-vehicle)
  • BS EN 60357: Tungsten halogen lamps (non-vehicle) - Performance specifications
  • BS EN 50285: Energy efficiency of electric lamps for household use – Measurement Methods

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