Artificial light can be a nuisance for many people, particularly astronomers. Bright lights at night cause glare discomfort, disability and loss of darkness, all of which creates problems for anyone who wants to admire the splendour of a clear night sky. And ‘obtrusive light’ isn’t just a nuisance for those at the eyepiece who’d like to be able to observe more stars; it can also have negative economic and ecological effects.
Sky-glow is the general, diffuse sheen visible in the direction of large cities, airports and industrial complexes. It occurs from both natural and artificial light sources and does not depend exclusively on lighting design, but also on atmospheric conditions.
Glare is the name we give to the uncomfortable brightness of a light source when viewed against a darker background.
Light can be propagated into the atmosphere either directly upward or from incompletely shielded sources.
It may also be reflected off the ground or other surfaces, partially scattering back towards observers and limiting the perceived darkness around them.
But lighting at night also has its uses, providing visibility and security around your home.
Luckily, there are lights designed for domestic use that will keep your property safe and won’t impact too much on your nightly observing.
Read more about light pollution:
- What can we do about light pollution?
- A guide to fighting light pollution
- How to remove light pollution from astrophotos
The science of light pollution
When observing the night sky, the human eye becomes nearly or completely dark-adapted, or ‘scotopic’. The scotopic eye is much more sensitive to blue and green light and much less sensitive to yellow and red light than the daytime-adapted, or ‘photopic’, eye.
Different light sources have different levels of apparent brightness to the dark-adapted eye.
White light sources such as metal halide, fluorescent or white LED can produce up to three times the visual sky glow brightness of a high-pressure sodium lamp.
Astronomers tend to use a red light source to view star charts, books and notepads in the dark, as this helps to protect night vision adaption.
Information printed in white text on black paper also helps maintain dark-adapted vision, because the light reflected back into the eye is considerably reduced.
Below we reveal four types of lighting that can be used for security and safety around the home and garden, including some examples of astro-friendly units that will preserve the darkness.
Domestic security lights should provide the minimum level of illumination to light a single property, not half the street.
Because of the price and ease of installation, many people install tungsten halogen floodlights, which can provide satisfactory security lighting. It is rarely necessary to use a lamp greater than 2,000 lumens (150W).
These lights can be fitted with detectors to sense the movement of intruders, but often the systems require the detector and the floodlight to be aimed in the same direction.
Blooma Pietas external security floodlight
- Manufacturer B&Q
- Price range £30-£40
Die-cast aluminium LED wall luminaire
- Manufacturer Lutec
- Price range £70-£110
Low-level bollard lighting can be useful for illuminating a garden path or footway to make walking to and from your house at night easier and safer.
However, if you’re wary of flooding your observing areas with light, it is important to consider the light distribution from these units and ensure that it’s directed downwards. This will avoid any glare towards the observer.
Owing to their short height and the local distribution of their light, you may need to space these units fairly close together.
Rusty Slot 50 outdoor post light
- Supplier SLV
- Price range £130-£270
Lucide combo outdoor LED post light
- Supplier Lucide
- Price range £60-£85
Another option is a bulkhead or porch light fitted with a low-power 600-900 lumen (9-11W) compact fluorescent lamp. These units can be left on all night, providing security for only a few pounds of electricity per year.
This light is also kinder to the environment, providing a gentle wash of light with reduced glare. Fluorescent lamps cast fewer shadows, reducing hiding places for criminals, and can be fitted with a movement detector if required.
These units are generally mounted lower and are therefore less likely to elicit complaints from neighbours.
LED Solar Flush wall light with PIR sensor
- Manufacturer Selected by suppliers
- Price range £14-£16
Ghost LED solar wall light with PIR sensor
- Manufacturer Lutec
- Price range £50-£75
When installing lighting to illuminate a large outside area, the same principles apply as with the positioning of domestic security lighting.
What you need to take into consideration is the height at which the lights will be mounted and the amount of distance between each of the lighting units.
For areas such as the garden, your driveway or other large external spaces, spacing the lighting units at around 2.5 times the height of the mounting should provide you with the correct lighting performance.
Kaskara area projector
- Manufacturer DW Windsor
- Price range £300+
- Manufacturer Schréder
- Price range price on application
Where to buy your lighting
Shopping around online is a good way to compare prices for the kind of lighting you want to buy. The following websites are a starting point:
Allan Howard is a past president and a current Fellow of the Institution of Lighting Professionals, with over 3 decades’ experience in the lighting business. This article originally appeared in the April 2018 issue of BBC Sky at Night Magazine.