Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.

Lamp selection

Lamp selection depends mostly on energy efficiency and the type and amount of lighting required.

On this page:

  • LEDs
  • Fluorescent lamps
  • Halogen lamps
  • Incandescent lamps
  • Recessed light fittings

The decision of which lamp to use is influenced by:

  • energy use
  • the amount of light emitted
  • lamp purchase cost
  • hours of lifetime use
  • application, e.g. task/general lighting, short/long periods of use
  • colour and temperature of the light required.

In order of lighting efficiency, from most efficient to least efficient, the available options are: light emitting diodes (LEDs); fluorescent lamps; halogen lamps; and incandescent lamps. As an example of the difference between the top and bottom of this range, a 9.5 W LED will produce the same amount of light as a 60 W incandescent bulb.


LEDs (light emitting diodes) are basically solid state devices like a semiconductor or circuit chip – there is no filament like an incandescent bulb, and no gas like fluorescent bulbs. LED light fittings are typically made up of a number of LEDs combined.

These are very energy-efficient with low heat output and are extremely long lasting – between 15,000–30,000 hours and more in some cases, compared to around 1000–2000 for incandescent bulbs. While LEDs should ideally be used in every room in the house, their long lifespan is especially useful in stairwells and other locations where bulbs are difficult to change. The only place they are not ideal is where they will be fully enclosed, for example in porch and veranda globes – they last longest when they have free air movement around them.

The LED lighting market has seen huge development in recent years, and now LED bulbs are available to replace incandescent or compact fluorescent bulbs in most existing fixtures and fittings, including spotlights and downlights.

Other LEDs are available with their own dedicated fittings. These are designed to maximise an LED’s lifespan by managing the heat that develops at the bottom of the lamp. If you are building a new house or making a significant renovation, these are a good option.

These lights turn on immediately, unlike some fluorescent bulbs that take a moment to warm up. Some LEDs are dimmable, and LED lights that produce a warm white light are available.

Fluorescent lamps

Fluorescent lamps:

  • are very energy-efficient, using as little as 20% of the energy to provide the same light output as an incandescent lamp
  • are long lasting (up to 10,000 hours)
  • can provide light in a range of colours.

They are not suitable for rooms where they will be used for short periods of time, such as toilets and bathrooms, because they need a ballast to start, which uses more energy than the light itself and causes extra wear. They also take some time to reach full brightness. They tend to be unsuitable for exterior use as they produce less light in low temperatures. Light output will drop slightly as fluorescent lamps age.

Fluorescent tube lamps:

  • are available in straight or circular styles
  • require special fittings
  • are good for background lighting but not for directional lighting
  • are most suitable for kitchens, garages and workshops and non-adjustable task lighting
  • have a separate replaceable ballast – although electronic ballasts are more expensive, they are more energy-efficient, longer lasting, start the lamp quicker, produce less flicker and are dimmable.

Compact fluorescent lamps are similar to fluorescent lamps but:

  • can fit into conventional bayonet or screw-fitting light sockets
  • come in a range of styles – stick, globe, circular and square
  • can replace incandescent light bulbs in most light fittings
  • have an integral ballast
  • should be concealed within a fitting to minimise glare.

They may not be able to be used with dimmers or sensors and electronic switches

Halogen lamps

Halogen lamps require special fittings and are more expensive than standard incandescent bulbs, but they last longer (up to about 2,000 hours of use). A 35 W halogen lamp produces the same light output as a 50 W standard incandescent. Low voltage halogen lamps (which need a transformer) will further improve energy efficiency but increase cost.

Halogen lamps have a compact filament to produce a concentrated light beam that illuminates a small area, making them suitable for highlighting or task lighting. They are a type of incandescent lamp but provide more light. IRC halogens are more energy-efficient than conventional halogens, with a lifespan of around 5,000 hours.

They are available in two voltages – 12 volt (which requires a transformer) and mains.

When specifying halogen lighting:

  • a whiter and brighter light is achieved with 12 V units
  • a softer light is achieved with mains powered halogens
  • 12-volt systems offer a range of special-purpose bulbs such as wide angle, narrow beam or coloured.

Linear halogen lamps should not be used where the source is visible to the occupants.

Incandescent lamps

Incandescent lamps are basically the same today as when they were invented over 100 years ago. Up to 95% of their energy output is radiated as heat rather than light. They are cheap to buy, but have a short lifespan (approximately 1000–2000 hours). The very low level of efficiency has led to the sale of incandescent lamps being effectively banned in many countries.

Recessed light fittings

Recessed downlight fittings in ceilings are a popular choice, but they can lead to three problems:

  • Insulation must be kept away from older models of these lights to prevent the lights, ceiling materials or insulation from overheating and causing damage.
  • A lot of heat can escape through holes cut in the ceiling for these older downlights, significantly reducing the effectiveness of ceiling insulation, and this can make homes hard to heat in winter.
  • The air that escapes from living areas into the roof space can carry a lot of moisture with it. If the roof space is reasonably airtight, this can lead to condensation forming on cold elements within the roof and a risk of mould growing on roofing timbers and roofing underlay.

Newer recessed downlights labelled IC and IC-F can be covered with insulation, reducing the risk of heat loss. Recessed downlights are also becoming available with features that reduce the amount of air (and moisture) movement from the living areas into the roof space.

BRANZ recommends replacing older downlights either with surface-mounted lights to avoid all heat loss, or with IC or IC-F recessed downlights that have insulation placed over them.

When it comes to updating these lights, replace the whole fitting rather than trying to just replace the bulb alone.


Updated: 25 January 2022