Guide

Lighting energy efficiency

Lighting system design

There are three main types of lamp, each of which creates light differently:

  • filament lamps - the filament has a high resistance to electricity and produces light when it gets so hot it glows
  • discharge lamps - an electrical charge applied to a gas-filled lamp makes the gas produce energy in the form of light
  • LEDs (light emitting diodes) - a pure semi-conductor produces light in response to an electrical current

Different lamps are appropriate in different situations. It's important to choose the right lamp for the right task when you're designing a new efficient lighting system.

Filament lamps

Incandescent tungsten filament lamps are widely used in homes and businesses. They give maximum light as soon as they're switched on and provide accurate colour rendering. However, they're relatively inefficient, have a short life and are expensive to run.

Tungsten halogen lamps use a filament in a gas-filled bulb. They are most suitable where spotlighting is required and are used in shops, museums, display areas and the hospitality sector.

Discharge lamps

Tubular fluorescent lamps are more effective than incandescent lamps and last much longer. Compact fluorescent lamps work in a similar way to fluorescent strip lighting but look like standard tungsten lamps. Both versions are widely used in offices and commercial buildings.

Low pressure sodium lamps are very efficient but they don't render colour well and take several minutes to reach full output. They're suitable for use in external areas like street lighting and car parks. High pressure sodium lights are similarly efficient and are particularly suitable for floodlighting large areas.

Metal halide lamps have low energy consumption and produce crisp white light. They're used in many industrial and commercial situations where good colour rendering is important.

Induction lamps have a very long life and are used both internally and externally - especially where access for maintenance is difficult.

LEDs

LEDs have a number of advantages, the most notable of which is their long life - potentially up to 50,000 hours. They are normally straightforward to dim and, unlike other lamps, their efficacy can improve when they are dimmed, as the lamp is running at a lower temperature.

Due to their long lifetime, LEDs are particularly suitable for applications where it is difficult to change lamps, although cleaning of the fitting still needs to be considered. LEDs can be used successfully within illuminated signs, such as emergency lighting.

The small size and directional qualities of LEDs means that they can also be used effectively for display lighting. However, when LEDs are used for general lighting, glare can be a problem.

LEDs have an instant start and do not flicker. Switching them on and off does not affect their life significantly, so they are also suitable for flashing beacons or for applications where frequent switching is likely, such as occupancy sensing in toilets, corridors or outdoor pathways. They are not particularly susceptible to vibration, so are suitable for automotive and aircraft applications.

To find out about the technical properties of different types of lighting download detailed guidance on efficient lighting systems from the Carbon Trust website (PDF, 7.3MB).

Energy efficient lamps

If you use fluorescent tubes you can make significant energy savings by switching to slimmer tubes. For example, if you replace T12 tubes (38 millimetres diameter) with T8 tubes (26 millimetres) you can make savings of 10 per cent. Switching to T5 tubes (16 millimetres) brings even greater savings while keeping a high light output.