Sky glow – is the unnecessary illumination of the sky above, and surrounding, an urban area. The sky glow created by Brisbane can be seen from hundreds of kilometres beyond the city. It is caused by multiple factors.

Poorly designed or installed luminaires can cast light directly into the sky if they are installed with a non-horizontal up-tilt, or are not designed to shield the light source above the horizontal.

Sky glow can also be caused by excessive levels of illumination on a reflective target area, resulting in light reflecting into the sky.

Sky glow can also be exacerbated by the use of light sources, such as high colour temperature LED, fluorescent, metal halide or mercury vapour street lights, that cast a substantial portion of their emitted light in blue wavelengths. Blue light wavelengths scatter and reflect off air molecules and dust much more than longer wavelengths – that is why our daytime sky is blue. At night, this blue light will scatter from above the city and extend far beyond the city and partially illuminate the night sky. It is this partial sky illumination that makes astronomical objects such as faint stars, nebulae and galaxies difficult or impossible to see within the city and surrounding regions.

Light spill – is light that unnecessarily illuminates areas beyond the target area. Due to reflection and/or refraction of light by components of a luminaire, light can “spill” beyond the target area. Light spill can also arise from poorly installed luminaires that are tilted above the horizontal. Light spill is wasted energy and becomes particularly problematic when it causes light trespass into nearby properties.

Glare – is a visual sensation caused by excessive and uncontrolled brightness of a light source impinging directly on the eyes of the observer. It can be disabling or simply uncomfortable. Glare from streetlighting is a particular problem when the line of sight is towards the light source and parallel, or approaching parallel, to the ray-path of the emitted light. When a pedestrian walks directly beneath a streetlight luminaire their line of sight is directed forwards and the source of light is from above, so glare is not experienced. However, when a pedestrian (or vehicle driver) approaches a luminaire from a distance their line of sight is towards the luminaire and rays of direct light will enter their eye. When the luminous intensity of the light is high, glare can be experienced.

Streetlight glare is primarily due to luminaires emitting too much light at high angles approaching the horizontal. Shielding of the light source above angles of about 70 degrees is essential to minimise glare.

Glare is defined technically in two forms – discomfort glare, and disability glare. Discomfort glare is the sensation of annoyance, or even pain, by an excessively bright light source the eye cannot adapt for. Squinting and turning away from the source are common consequences. Such glare may also make a task, such as walking, more difficult and reduce the ability to see into shadowed areas.

Disability glare is the reduced visual performance and visibility caused by the action of stray light, which enters the eye and scatters within. It causes a ‘veiling luminescence’ over the retina, which, in turn, has the effect of reducing the perceived contrast of the objects being viewed. Disability glare can make a task extremely difficult or impossible.

Poorly designed or installed luminaires can radiate directly from the primary beam of a luminaire, or due to reflection and/or refraction of light by components of the luminaire. Light spill can also arise from poorly installed luminaires that are tilted above the horizontal. The consequence can be excessive glare for pedestrians and vehicle drivers and annoying light trespass into homes across the street or behind a street light.

Glare can also be exacerbated by the use of light sources with a high colour temperature, particularly above 3000K colour temperature where blue wavelengths constitute a significant proportion of the total emitted light. Blue wavelengths will scatter within the human retina more than longer wavelengths. It is this scattered light that creates the ‘veiling luminescence’ problem.

Light pollution is a waste

If street or commercial lighting is casting light into nearby properties, or the sky, it is wasting energy and contributing to increasing atmospheric carbon dioxide. Public lighting blazing at full capacity throughout the night, when it is only at its most beneficial for the initial evening hours, is also wasteful. Property owners and ratepayers pay the financial bill for this waste.

What price do city residents place on a good night’s sleep? Why should resident be expected to endure the intrusion public lighting into their homes? The loss of the night sky aesthetic is another cost incurred by the community within the city and surrounding areas. Is there a cost to a child from never seeing the night sky in its true starry wonder?

It is easy to ignore light pollution. However, our night sky and residential streets will just get brighter if we do. Public pressure is the only force the people we elect take heed of. If you feel light pollution from public and commercial lighting is a problem, you should contact our local and state government representatives and prompt them to act. If we do nothing, they do nothing.