Illuminating Facts about Lamps
There are several categories to consider when selecting lamps typically used in domestic, commercial and industrial settings. Here we provide a breakdown of the types of lamps available, and the factors which separate them.
- What are the most common types of lamp?
- Which type should I use?
- What is colour temperature?
- What is colour rendering?
- What is luminous efficacy?
- How can I access life expectancy?
What are the most common types of lamp?
General Lighting Service (GLS) and Reflector Filament Lamps are mostly used for domestic and display lighting, commonly GLS and Decorative, in clear, pearl or coloured, and with reflective coating for reflector lamps. Low cost and easy to use but only half the life of standard lamps and sensitive to voltage variations.
Halogen–filled filament lamps (tungsten halogen) have a longer life and/or more light output than standard lamps. Halogen gas prevents evaporated tungsten from blackening the lamp’s small, quartz or hard glass envelope.
Low pressure mercury fluorescent tubes now offer higher efficiency and longer life, improved lumen maintenance and colour rendering than previous tubes. Their light ouput comes from phosphors which convert energy from a low pressure gas discharge into visible light.
Compact Fluorescent Lamps (CFL) are similar to a linear fluorescent lamps but more compact and efficient due to the discharge path being folded. With external or international control gear, integrated high frequency control gear is now available enabling simple conversion from GLS to CFL. The decreased gear weight and size enables higher efficiency, silent operation and dimming.
High pressure sodium lamps are used for lighting roads, floodlights and as commercial lamps for industrial interior lighting. Light comes from an electrical discharge in a gas containing sodium and mercury in a tube. De Luxe types offer improved colour rendering but are less efficient than standard lamps. Come marked with an I if they have an internal ignitor, and E if external.
Low pressure sodium lamps are mostly used outdoors, for roads and security. They come in the form of a U tube which contains the discharge, with an outer jacket which reflects heat. Although it is the most efficient of all lamp types, its colour rendering is poor and it is not suitable for repeated switching on and off.
Metal halide discharge lamps are usually used in commercial and/or retail interiors, for floodlights and in industry. Featuring quartz or sintered alumina (ceramic) arc tubes, mostly with an outer glass envelope, light output is created by mercury and other metallic elements introduced through halides. Protected types are now available for lighting without safety screens.
High pressure mercury discharge lamps have mostly been replaced by more efficient lamps but used to be used for illuminating road signs and industrial lighting. Can still offer low cost discharge where high efficiency is not a key issue.
Induction lamps are available as low pressure mercury lamps, and the range of commercial bulbs is limited. Induction works by passing electrical power from one circuit to another without physical electrical conductors, eliminating the need for wire connections passing through the glass or quartz envelope.
Light emitting diodes (LEDs) have a very long life and are a component as opposed to an end user product. Used in an increasing number of applications there is an extended range of sizes and colours, efficiency levels are expected to increase extensively.
Which type should I use?
Selection criteria for types of lamps include:
- Capital and running costs
- Colour temperature
- Colour rendering
- Luminous efficacy/energy efficiency
- Service period
- Lamp dimensions
- Luminous flux
- Re–strike recovering time
- Capacity for dimming
- Cost of replacement
What is colour temperature?
This is a measurement used to define whether the lamp has a warm, intermediate or cool appearance, and is described in Kelvin (K). Warm lamps have a colour temperature of below 3500K, intermediate range from 3500K to 5300K, cool is between 4000K and 5300K, whilst cold bulbs rate above 5300K.Start of page
What is colour rendering?
In order to reproduce the correct colour of coloured objects, the light that falls on them must contain components capable of doing this. This ability is measured by the Commission International de L’Eclairage (CIE) general colour rendering index (Ra). A value of 100 represents perfect colour rendering.
This index falls into the following classes:
- 1a, with index Ra > 90, where accurate colour matching is required, e.g. printing.
- 1b, with index 90 > Ra > 80, where colour must be good for aesthetic purposes, e.g. in shops.
- 2, with index 80 > Ra > 60, where moderate colour is required.
- 3, with index 60 > Ra > 40, where accurate colour is not so important but must not be distorted.
- 4, with index 40 > Ra > 20, where colour and distortion are of no importance at all.
What is luminous efficacy?
This is the ratio of light input (lumens) to lamp power (Watts), and should be considered when designing lighting.
The conservation of fuel and power is regulated under Part L of the Building Regulations for England and Wales, with subsection L1 covering dwellings, and L2 covering other buildings.Start of page
How can I access life expectancy?
The service period for filament lamps and fluorescent discharge lamps differs according to various factors.
- For filament lamps is the average amount of time between installation and when they stop working, with the lifespan decreased by heat, vibration, lamp orientation and high supply voltage.
- For fluorescent and discharge lamps it is the average amount of time taken for the light output to deteriorate to a level where it would be more cost–effective to replace them.