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.
Natural light enables artificial lighting to be switched off to save energy.
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.
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 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
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.
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?
Carbon Trust Lighting
Technology Overview (CTV021)