Avoid obtrusive light

This Issue This is a part of the Exteriors and interiors feature

By - , Build 166

Whether intruding into the interior of a building or washing the exterior, obtrusive outside light is annoying. While in some situations people may just have to learn to live with it, often it can be mitigated or avoided.

OBTRUSIVE LIGHT is an avoidable form of pollution. It is wasted light and, as such, the owner of the light is wasting money paying for light that is going where it is neither required nor desired. Avoiding it is therefore a win-win situation.

Range of obtrusive light

Situations where obtrusive light may occur include:

  • spill light — also known as light trespass
  • glare
  • sky glow, which causes loss of night sky visibility
  • headlight sweep — intermittent flashes of light disrupting amenity
  • sign and façade brightness, which intrudes into landscape views
  • flashing or strobing lights
  • built structure interior light glow in an otherwise dark environment.

The most common of these effects are spill light and glare.

In most instances, obtrusive light effects are those impacting residential locations where the residents are regularly subjected to the effects (see Figure 1).

Where the same effects are experienced by an occasional visitor, such as someone spending a night in a hotel, the impact is considerably less.

Spill light

Many people think of spill light, measured in lux, as being the most important consideration. However, it is unlikely to be of concern unless it intrudes inside a house. It does need to be controlled and avoiding obvious spill light onto the façade of a house is desirable.

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In most situations, glare is by far the greatest potential issue. People in residential situations generally have no particular interest in how much light is falling on their fence, but having to look out every night at glary lights is a distinct loss of amenity.

There will be exceptions, such as roadway lighting, where public safety needs may result in some unavoidable residential glare. However, in most situations, the effects can be avoided or mitigated.

LED lights have many benefits

Almost all light fixtures produced now are available as LEDs. LEDs have come of age, and in virtually every situation, they represent the most energy-efficient solution.

LEDs have the potential to be a more precise tool, delivering light only where it is needed. The downside is that this can increase potential issues for crime prevention, such as by making dark areas close to trafficable areas even darker.

Another downside is that powerful LED chips can be extremely bright and generate greater glare effects than similar light fixtures with older technology.

Blue-rich light may be a concern but depends on dosage

There has been a lot of press in recent years suggesting that the blue-rich light typically produced by exterior LEDs is of particular concern for sleep disruption and possibly other health concerns. While that may be true, it depends on dosage. The dosage typically received from outdoor lighting is only a small fraction of that received from other sources such as indoor lighting and computer screens.

A similar proportion of blue-rich light is also produced by technologies that have been used for decades, such as fluorescent, metal halide and mercury vapour.

There are controls in place

In most situations, obtrusive lighting effects are controlled by the relevant local district plan. These typically contain rules specific to outdoor lighting, although the level of detail, quality and effectiveness of the rules vary significantly throughout the country. The most effective plans are based on standards such as AS 4282-1997 Control of the obtrusive effects of outdoor lighting.

Face external light fixtures downwards

Wherever possible, a good rule of thumb is to use full cut-off lights (i.e. no direct upward light) and install with no upward tilt so they don’t project any light above the light fixture. This simple act will resolve many potential obtrusive light issues.

Modern technology has given us light fixtures that can project light forward asymmetrically, so with a suitable mounting height, there should seldom be a need to tilt the light fixtures to get the light where it is needed.

Even so, if there are houses nearby at a lower elevation than the lighting installation, they could have a view into the glarier parts of the light fixtures.

There are some light fixtures that cannot be aimed down, such as wall lights, signs or uplights, and some that need to be tilted to achieve the desired result.

Seek independent advice

Lighting design is a technical skill understood by a small group of practitioners and illumination engineers. When seeking advice, use a professional who fully understands obtrusive lighting and how best to satisfy the statutory requirements.

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For more

Further information is available from the International Dark-Sky Association at www.darksky.org.

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