What is it?

Even though nighttime outdoor lighting is an important controllable aspect of our environment, it is not well understood. Most outdoor lighting decisions are made without any knowledge of the physiology of human vision, sound illumination engineering principles, light fixture alternatives, or life cycle costs. Therefore, poor quality outdoor lighting is seen everywhere in our community, particularly in the commercial and residential sectors. Poor quality lighting results in the following problems: glare, light trespass, uplight, overlighting, and energy waste. Let's examine these five areas.

GLARE is defined as: "the condition of vision in which there is discomfort or a reduction in the ability to see significant objects, or both, due to an unsuitable distribution or range of luminance." As we age, problems with glare worsen. If a light source (bulb) is more noticeable than the objects it is illuminating, then the source is producing glare. When glare is minimized, less light is needed to see well, thus saving energy and natural resources (coal and oil) in the process. We always see better in the absence of glare; minimizing it also results in a more attractive nighttime environment.

LIGHT TRESPASS, also known as spill light or obtrusive light, is light that falls where it is not wanted or needed and often results in glare. Examples include: street lights shining directly into residential windows, business lighting shining into residential areas, and residential security lights shining onto adjacent properties or even into windows. Light trespass results in visual clutter and confusion, particularly in commercial areas. Good quality outdoor light fixtures have good optical control so that the light is directed only where it is needed.

UPLIGHT is light that leaves a fixture at or above the horizontal plane through the fixture. Uplight is wasted light serving no useful purpose. It never reaches the ground. Not only are energy and natural resources wasted, but the night sky - an important part of our natural heritage - is obscured. City dwellers can no longer enjoy the natural phenomena our ancestors knew so well: a star-filled sky, the Milky Way, meteor showers, just to name a few. The brightness of the night sky is due primarily to direct uplight, not light reflecting off the ground. Uplight should not be tolerated. Light fixtures which produce no uplight, called full-cutoff, are readily available. By eliminating uplight and near-horizontal light (which causes glare), lower wattage bulbs can be used to provide the necessary ground illumination levels, thus saving energy, money, and natural resources.

OVERLIGHTING occurs when illumination levels are higher than recommended. The human eye naturally adapts to a lower light level at night than in the daytime. Visual performance is excellent at lower light levels, especially when glare is eliminated. Different tasks require different light levels, and the Illuminating Engineering Society of North America (IESNA) has defined minimum recommended levels for various situations. Their comprehensive and ongoing testing has shown what light levels are best. Lighting should not exceed these recommended levels. Overlighting provides no benefit, wastes energy, and lessens visual performance by increasing discomfort glare and disability glare. It also makes less-well lit areas seem darker, because night vision is destroyed.

ENERGY WASTE occurs whenever our lighting produces glare, uplight, light trespass, and overlighting. It also occurs when we use inefficient light sources. Currently, high pressure sodium (HPS) and low pressure sodium (LPS) are the most energy efficient light sources available and they should be used in all situations where a high degree of color accuracy is not needed, as is the case with most outdoor lighting tasks. In situations where color accuracy is critical, such as some sports lighting and automobile dealership lighting, metal halide (MH) is the best choice. But it should not be used indiscriminately. Not only is it less energy efficient than HPS and LPS, but the bluish light makes it harder to adapt to changing light levels as one moves from well lit to lesser lit areas. The orange light of the HPS and the yellowish light of the LPS are less likely to diminish the ability to see in low light levels. Some installations have used a combination of HPS or LPS with about 10% added MH light, giving efficient lighting with improved color recognition.

Clearly, we need outdoor lighting at night for safety, utility, and security. But glare, light trespass, uplight, overlighting, and energy waste should not be tolerated. Outdoor lighting decisions made today will affect the kind of environment we will live in for many years to come.