Understanding Light Distribution

It is important to understand the concept of light distribution to maximize effective illumination of an area without under-utilizing its output. In identifying the output of light produced by an outdoor fixture, we observe different light distribution types—the light pattern of a light fixture.

Type I distribution is linear and ideal for narrow walkways or bike paths. It is meant to be placed near the center of a pathway and the concentration of light is spread in opposite directions. The diagrams below show applications of Type I light distribution.

Type II distribution accommodates to wider, larger areas and is typically located near the roadside where the width of the road does not exceed 1.75 times the designed mounting height. It is ideal for wider walkways, entrance roadways, bike paths, on ramps, as well as other long, narrow lighting applications. This type of lighting can also be found on smaller side streets or jogging paths.

Type III distribution, also known as “Bat Wing”, is ideal for roadway, general parking areas, and other areas where larger area of lighting is needed. This type of lighting is suitable to be placed at the perimeter of areas because it projects light outward filling the area. It is important to note that the width of the area or roadway for this type of lighting must not exceed 2.75 times the mounting height.

Type IV produces a semicircular light that is suited for wall mounting applications and illuminating the perimeter of parking areas. This distribution is also called the “Forward Throw”, which means it provides sharp house-side cut-off and can be used for perimeter lighting applications with minimal spill light. It is intended for side of road mounting and is generally used on wide roadways.

Type V distribution can produce circular patterns or square. In both distribution types, the light intensity is the same at all angles. This distribution is best suited for interior areas within a site, like large parking areas, or the medians of roadways with 4 to 6 lanes or even intersections. The square light pattern is used when an area needs a more defined edge.