Light distributions tell you the pattern of light that comes out of the fixture and forms on the ground. Determined by the Illuminating Engineering Society (IES), light distributions give landscape architects and lighting designers a tool to properly light a site.

Since a site may have multiple lighting needs, from broadly lighting a parking lot, for example, to lighting a narrow pathway, multiple light distributions allow designers to target the need with the correct distribution. Landscape Forms Lighting Sales Specialist explains that a lighting product line with multiple distributions “give designers peace of mind. They have flexibility to use the same light product from the building to the parking lot and maintain a design aesthetic.” How a distribution throws light is important in eliminating trespass and wasted light.

There are five light distributions, the Lighting Sales Specialist explains each and the types of applications for which they would be specified.

Type I and Type II are similar in that they throw a narrow and linear light pattern. These distributions are used mainly on pathways, walkways, and sidewalks where a side-to-side throw of light is desired. Type I and Type II distributions are great for spacing and keeping light on walkways and out of the landscape. Type II distribution has a little more forward throw compared to Type I.

Type III offers side-to-side light but also more forward throw than a Type I or Type II distribution. This distribution is used in areas that are larger and need more coverage. Because it has both side-to-side and forward throw, applications for this distribution are versatile and broad. It can be used along the edges of a site because its asymmetric pattern throws light forward and helps reduce backlight.

Type IV typically features the most forward throw among the asymmetric distributions. This distribution is often used in places such as parking lots where there may be limited pole locations and a need to illuminate far-reaching areas.

Type V is a symmetric distribution that throws light equally in all directions. It is often used on a fixture in the center of an area and in catenary applications. Type V can be circular or square.

Both distribution and fixture height come into play when properly lighting an area. That is why fixtures with multiple distributions, pole heights, and lumen outputs are important. The IES has recommendations on uniformity for different applications, and the heights you use will affect those uniformity levels.