Natural Light

  • 4 Jun 2015

What are they?

Natural light most commonly enters a building through windows but may also enter by other means such as skylights, atria, solar tubes (which take light from roof level into single storey buildings) and south lights. Natural light can be used to supplement artificial lighting, or wholly replace it for much of the day. Any obstructions outside the window, such as buildings or trees, will reduce how much natural light enters a building.

Advantages / Disadvantages

Reduces the amount of electricity consumed to provide  general and task lighting.

Natural light has a health and wellbeing benefit for staff.

Direct sunlight can cause glare and ‘solar gain’, which increases the cooling demand in a space.

Setting up effective daylight controls in a complex space such as an office can be remarkably difficult, so energy savings are often not achieved.

Energy efficiency

Natural light enables artificial lighting to be switched off to save energy.

Running costs

Natural light provides a cost saving from the reduced use of artificial lighting. Lighting controls can be provided which automatically adjust artificial lighting to reflect the amount of natural light entering the space. Large north and west facing windows may result in additional  energy consumed for cooling during summer months due to solar gain.  West facing window are prone to glare from low-angle late afternoon sun.  Similar issues can occur with east facing windows, but these tend to occur prior to normal occupancy hours.

Note that running costs will only be reduced if artificial lighting is reduced in response to natural light levels; no savings will be made if artificial lights continue to operate unchanged.  It is generally easier to configure daylight control to work in less sensitive areas such as lobbies and halls  than in offices.

Retrofit / improvement opportunities

Increasing window size and introducing atria are costly and impractical.  Retrofitting sun-pipes or north lights into the roof of a single storey  building or the top floor of a multi-storey can be practical solutions.

Applicable buildings

All building types.

Floor plate implications

Natural light entering through a window diminishes across a deep floor  plate. Sky lights, atria or sun-pipes can be used to provide natural light  to internal spaces although these have implications on building form  and configuration.

Occupant comfort

Occupant health, wellbeing and productivity benefits are often cited for  buildings with high levels of natural light compared to those with limited  natural light or entirely lit using artificial lighting.  However window glare and direct sunlight must be well managed to achieve these outcomes.

Lighting control in office spaces must be very well managed to avoid becoming an irritant to staff.  Typically this means that dimming is required, rather than switching on and off, and

Maintenance implications

Windows need to be cleaned regularly as dirt will reduce the light entering the building.  Daylight-linked control systems require careful design, commissioning and maintenance to operate successfully.

Identification

Sufficient natural light in a building is the point at which tasks can still be performed if the lights are off.

Questions to ask

  • are controls in place to dim or switch off  Is artificial lighting regularly switched off during the day because    natural light is sufficient to perform tasks?
  • Are there areas of the building where solar glare is a problem during    the year?

More information

Carbon Trust Lighting

Technology Overview  (CTV021)