Lighting and daylight

DaylightWhy it matters

Daylight is the best light there is. It shows true colours, it changes through the day, and it helps set the body clock that governs sleep. Morning light in the kitchen and living areas helps people wake. Warm, dim light in the evening helps them wind down. A house planned around daylight also needs its electric lights less often.

The code sets a minimum. Every habitable room needs windows with a clear glass area of at least 10% of its floor area, or roof lights of at least 3%. Roof lights can be smaller because they see more of the sky. A 20 m² living room therefore needs at least 2 m² of clear glass. That's the minimum for a legal room, not for a well-lit one.

Getting it deepRoom depth, window height and two-sided light

How far daylight reaches depends more on where the window sits than on how big it is.

• Room depth. Useful daylight reaches roughly two to two and a half times the height of the window head above the floor. With a window head at 2.1 m, the back of a room more than about 5 m deep will feel dim, however wide the window.
• Window height. Raising the window head, or adding a highlight window above it, pushes light deeper. Light coming in high bounces off the ceiling and spreads evenly.
• Two sides. A room with windows on two sides gets more even light and much less glare, because the bright window no longer sits against a dark wall. Corner windows and clerestories do the same.
• Light surfaces. Pale ceilings, walls and floors reflect light back into the room. Dark finishes absorb it.
• Borrowed light. Halls, stairs and bathrooms in the middle of a plan can take light from neighbouring rooms through highlight glazing, glazed doors or open stairwells.

Daylight and heat travel through the same glass, so these choices go together with orientation, glazing and shading. North windows with well-sized eaves give generous light and welcome winter sun. South windows give soft, even light without glare, which suits studies, studios and kitchens. East and west windows bring low sun deep into the room, with glare in the eyes and heat on the floor, so they need external shading or should be kept small.

SkylightsLight from above, with care

A skylight lights the middle of a plan where no window can reach. It also faces the hottest sky in summer and the coldest sky on winter nights, so a large one can overheat a room by day and lose heat all night.

• Keep them small. A modest skylight lights a surprising area, because it sees so much of the sky.
• Put them where they count. Halls, bathrooms, walk-in robes and the back of deep kitchens benefit most.
• Consider tubular skylights. A reflective tube brings in plenty of light with very little heat gain or loss, and it suits small rooms well.
• Mind the shaft. A deep, narrow shaft loses much of the light. Splay it, or line it with a light, reflective finish.
• Specify performance. Double-glazed units with good frames, and blinds or diffusers on larger ones. The code limits roof lights and sets performance requirements for them, and the energy rating counts them.
• Watch for condensation. A cold skylight in a Canberra winter is a classic place for water to collect and drip. Insulate the shaft and keep it airtight.

Electric lightingLess power, better placed

Electric lighting is now a small part of a home's energy use, as long as the fittings are efficient and the switching is sensible. LED lights use about 75% less electricity than halogen globes for the same light and last five to fifteen times longer. The code limits the lighting power for a house to about 5 W per square metre of floor area, and the NCC Whole of Home rating counts it.

• Layer the light. Use general light for moving around, task light where people cook, read and work, and lamps for evening. A few good fittings in the right places beat a regular grid of downlights.
• Choose the colour. Warm white suits living rooms and bedrooms. Cooler white suits kitchens, studies, laundries and workshops. Blue-rich light late in the evening can upset sleep, so keep bedside lighting warm.
• Switch by zone. Separate switches for each part of an open-plan room let you light only what you're using. Dimmers help set the mood and save energy.
• Use sensors where they help. Motion sensors suit laundries, walk-in robes, garages and outdoor paths, where lights get left on.

Mind the ceiling. Every recessed downlight sits in the ceiling insulation. Unless the fitting is rated to be covered, the insulation has to be kept clear of it, and those gaps add up quickly across a house. Use fewer recessed fittings, choose ones rated to be covered by insulation, or use surface-mounted and pendant lights that don't break the ceiling at all.

OutsideLight where it's needed

Outdoor lighting should light paths, steps and entries for safety, and do little else. Point fittings down, shield them so the light falls on the ground rather than into neighbours' windows or the night sky, and use motion sensors or timers so they aren't left on all night. Warm-coloured, low-level light is also kinder to people trying to sleep next door.