Energy

When designing a lighting scheme for a home, energy efficiency can be enhanced by:

• avoiding over-lighting
• specifying energy efficient lamps
• specifying appropriate lighting for the purpose
• designing lighting to give precise control so lights aren’t on when they’re not needed.
• In New Zealand, the energy consumed by all lighting is around 3 TWh per annum (EECA 2004). This results in greenhouse gas emissions of around 1.8 Mt of CO2 (based on electricity emissions factor presented in NZCCO 2003) or 2.4% of New Zealand’s total gross greenhouse gas emissions.

Appropriate lighting levels

The level of light on a surface is called illuminance. It is expressed as lumens per square metre or lux. In determining the appropriate amount of lighting, you’ll need to consider:

• the passive design daylighting provided by the design of the building
• direct lighting from lamps
• reflected light – levels will be higher from lighter-coloured or glossier surfaces.
• Good lighting design is said to be lighting that “allows you to see what you need to see quickly and easily and does not cause visual discomfort but does raise the human spirit”.

Insufficient light levels can be uncomfortable and unsafe. Too much light can cause glare, which is also uncomfortable and can cause headaches or eyestrain. And too much artificial lighting wastes energy.

New Zealand Building Code Clause G7 Natural Light requires 30 lux of natural light at floor level for 75% of the year. Clause G8 Artificial light requires 20 lux of natural or artificial light at floor level at all times when the room is inhabited. Though energy efficiency can be maximised by providing no more than the minimum level of lighting required, this may not always be safe or comfortable.

Recommended lighting levels are:

• 150–200 lux for general household activity – for example, vacuuming or washing
• 300–500 lux for focussed activity – for example, reading or studying, working on a car
• 750 lux or more for concentrated activity – for example, fine detail sewing. 

Adjustments should be made to these recommended lux levels so they are:

• higher – if there isn’t much reflected light, or levels of light and dark contrast are low, or the area has no windows
• lower – if the task is of short duration.

Appropriate lighting for the purpose

The design of a lighting installation within a home needs to accommodate a range of functions and activities.

Generally, lighting within a home can be broken into:

• general lighting to provide an all-over low level illumination of a space
• task lighting to illuminate an area (desk or benchtop) where a higher lighting level is required (Task lighting is more effective where lower wattage lights with a focused light beam are specified. Task lighting can create issues of glare, flicker, noise or heat output.)
• accent lighting to highlight decorative or dramatic features using spotlights or wall washer lights.

Switches, dimmers, timers and sensors

Switches

For general space lighting, locate switches at room entry and exit points. Specify two- or three-way circuits where a space has multiple entry points and for stairs.
For task lighting and accent lighting, locate the switches adjacent to the task area. That way, occupants won’t be tempted to turn on task lights when they’re not needed. An alternative is to locate task and accent lighting on a single control panel remote from the general lighting switch.

Each lighting installation should have its own control. Having one switch point that turns on all lights in a room will lead to wasted energy.

Movement sensors

Movement sensors turn lights on automatically when someone comes in to a space and turns lights off (either by movement or after a set period of time) when the person leaves. This can reduce energy wastage. Movement sensors use a small amount of power by being on standby, but this is much less than lights that are left on continuously.

Specify movement sensors that:

• incorporate a daylight sensor and/or timer so lights don’t turn on unnecessarily
• have a manual over-ride function.

Dimmers

Dimmers can save energy and increase bulb life by reducing light output. Specify a dimmer linked to a photoelectric light meter to reduce artificial lighting when more natural lighting is available.

Timers

Delay timers can be specified to switch lights off automatically after a short period. This saves energy by ensuring that lights aren’t left on indefinitely, but can also cause safety issues if the light goes off without warning. Timers are more suited to spaces that are only used for short periods of time, such as toilets or store rooms. Schedule or programmable timers can also be used to turn lights on and off at particular times of the day or week. Specify models that have a manual override.

Programmable/automatic lighting

Higher cost lighting options include fully programmable or automatic house lighting systems that will operate light and security systems to maximise operating efficiency.

For your clients

To help your clients make decisions about lighting options, refer them to www.smarterhomes.org.nz/energy/lighting.