Artificial lighting is important to many aspects of modern life. For example, artificial lighting can be important for many different sporting competitions and sporting venues. While artificial lighting often allows participation in indoor sports, and outdoor sports in darkened conditions, artificial lighting is not without drawbacks. Glare is currently one of the biggest complaints about sports lighting. The problem of glare is not limited to sporting venues either. For example, flood lighting used around various structures and airport ramp lighting are often the subject of complaints about glare.
Glare and related light trespass are of special concern when installing floodlights. Disability glare reduces visual performance and visibility. Discomfort glare produces physical discomfort. It is possible to experience disability without discomfort, and conversely, discomfort without disability, however, one often accompanies the other. Regarding light that we actually see, brightness can be measured as the light leaving a lamp, or the light reflecting from an object's surface. It is measured in footlamberts (English) or candelas/square meter (metric). In practice, glare is usually a situation where a source of unshielded light is at least 1,000 times brighter than the average visual field. For instance, because the night sky is dark, almost all outdoor light sources, such as a street luminaire or automobile headlight, cause glare. To evaluate glare, however, one may use luminance, which typically is measured in candelas per square meter (cd/m2) or nits.
As used herein, the term glare includes all forms of glare, including discomfort glare and disability glare, as well as light trespass, and related stray light problems. For example, ocular stray light is a phenomenon where parts of the human eye scatter light that reaches the retina, but do not contribute to forming a correct image.
One approach to reducing glare is to decrease light intensity of the artificial light source. However, if the decreased light intensity cannot be offset with additional lighting fixtures, overall lighting may drop below acceptable levels. Even if decreased light intensity is offset with additional lighting fixtures, such additional lighting fixtures typically incur a corresponding increase in costs.
Another approach to reducing glare is to use louvers, such as various types of blade and concentric louvers. Unfortunately, louvers have the effect of reducing light output and correspondingly increasing costs to compensate for the loss of light by producing additional lumens of light to offset the losses.