Outdoor Lighting at Home and the Night Sky

The light that hides the Milky Way from suburban New Zealand doesn't come only from street lights and stadiums. Homes add their share: floodlights left on all night, unshielded deck lights, garden uplights pointing at the sky. The good news is that home lighting is also the easiest kind to fix, and most of the changes save power too.

The places that have earned dark sky status in this country, described in our post on dark sky places in New Zealand, got there partly through ordinary households changing their outdoor fittings. The same principles work in any backyard.

The five principles

Most dark-sky lighting advice comes down to five questions to ask of any outdoor light:

1. Is it useful? Does this light need to exist at all?
2. Is it targeted? Does it shine only where the light is needed?
3. Is it low level? Is it no brighter than necessary?
4. Is it controlled? Is it on only when needed?
5. Is it warm-coloured? Does it avoid blue-rich white light?

Dark Sky NZ and the reserve communities promote much the same approach. It is simple enough to apply room by room around the outside of a house.

Shield it and aim it down

A bare bulb or a clear-glass lantern throws light in every direction: sideways into neighbours' bedrooms, upward into the sky, and straight into the eyes of anyone walking toward it. A fully shielded fitting has an opaque top and sides, so the bulb itself can't be seen from beyond the area it lights. The ground gets the same light, the sky gets none, and the glare disappears.

Aim matters as much as shape. A floodlight tilted up to reach the far corner of a section sends a beam well over the fence. Pointing it down and moving it closer to what it needs to light nearly always works better.

Choose warm colour

Blue-rich light scatters more in the atmosphere, contributes more to skyglow, and has a stronger effect on wildlife and on our own sleep. When buying LED fittings or bulbs, check the colour temperature on the box:

• 4000 K and above: neutral to cool white. Best avoided outdoors.
• 3000 K: the upper limit DarkSky International recommends for outdoor lighting.
• 2700 K: warm white, a better choice.
• 2200 K or lower: amber. Ideal for paths, decks and anything near bush or the coast.

Amber light looks perfectly natural around a house once you are used to it, and it helps your eyes keep their dark adaptation if you step outside to look at the sky.

Use the lowest useful brightness

Modern LEDs are so efficient that it is easy to overdo it. Lower-output fittings often make a space feel safer, because there is less contrast between bright pools and dark shadows. EECA has useful general guidance on efficient lighting and running costs.

Control it: sensors and timers

A motion sensor turns an all-night floodlight into one that runs for a few minutes a night. A timer or dusk-to-midnight setting does the same for decorative lighting. Set sensors so they don't trigger every time a cat crosses the lawn or a car drives past.

Wildlife

Artificial light at night affects far more than astronomers.

• Seabirds. Fledgling petrels and shearwaters leaving coastal colonies for the first time can be drawn to bright lights and grounded. Coastal communities in several parts of the country run campaigns each year asking residents to turn lights down during fledging season.
• Kiwi and other nocturnal birds are adapted to darkness, and artificial light can disrupt their feeding and movement. Homes bordering bush can make a real difference here.
• Insects are drawn to blue-rich light in enormous numbers and many die around fittings. Warm, shielded light attracts far fewer.

Room-by-room checklist for the outside of a house

Soffits and eaves. Recessed downlights in the soffit are usually fine if the lamp sits up inside the fitting and doesn't poke below the lining. Avoid surface-mounted globes.

Decks. Low step lights and recessed riser lights put light where feet go. Skip the overhead floodlight. If you use the deck for stargazing, a separate dim red or amber circuit is worth having.

Paths. Bollards with downward-facing louvres, or small ground-level lights angled across the path, give safe footing without glare.

Driveways. One shielded fitting on a motion sensor at the garage, aimed down, usually does the job.

Security lights. Fit a sensor, aim it at the ground near doors and gates, and choose a lower-output model. A dazzling floodlight creates deep shadows and blinds the person looking out.

Gardens and facades. Avoid uplighting trees and washing walls with floodlights. Most of that light carries on past the target into the sky. If you want feature lighting, keep it low, warm, shielded and on a timer.

Neighbours. Stand at your boundary at night and look back at the house. Any bulb you can see directly from there is causing glare.

A good moment to rethink

Lighting is easiest to change when other work is already happening on the outside of a house. A repaint, new cladding, re-roofing or a deck rebuild usually means fittings come off the walls anyway, and electricians may be on site. It costs little extra at that stage to swap globes and floodlights for shielded, warm-coloured fittings, add a sensor or move a light lower. Some of these changes involve wiring and must be done by a licensed electrician, so add them to the plan early.

Why it matters here

New Zealand still has large areas of genuinely dark sky, and the southern Milky Way is among the finest sights in astronomy. Skyglow spreads a long way beyond the towns that cause it. Every shielded, warm, well-timed light helps keep that view for the people next door and for whoever comes after us.