Lighting distribution: it’s a key factor that is frequently overlooked when we are choosing the proper LED luminaires (especially for outdoors). In the industry lighting, we think about the wattage, efficacy, and colour temperature, but usually forget to consider the way light is distributed from the luminaires. Will the chosen luminaires adequately cover the area we are trying to illuminate based on the position it will be installed? This is where understanding IESNA Distribution Types will help us make a good choice. 

IESNA Light Distribution:

To help lighting specifiers choose the proper fixture for their application, the Illuminating Engineering Society of North America (IESNA) introduced a classification system for light distribution patterns. The system consists of five “Types” (Type I – Type V) that makes it easy to identify the distribution pattern of a fixture and correctly match it to the right application.  

Understanding IES Distribution Types 

Here are the main differences between each IES Distribution Type and the types of applications they are best suited for:

• IES Distribution Type I 

Type I distributes a very lineal shape. It is the optimal choice for applications such as one or two-lane roadways, walkways, paths or sidewalks. With a preferred lateral width of 15 degrees, it is suitable for lighting streets or pathways that have a width of up to 2 times the mounting height. 

• IES Distribution Type II 

For Type II, the shape is still linear but is wider in the front. With a lateral width of 25 degrees, it is the ideal choice for wider walkways, entrance roadways, on-ramps, four-lane roadways or any area requiring long, narrow lighting. When considering area width, Type II is best for illuminating areas with a width that are no more than 1.75 times the height the fixtures will be mounted. 

• IES Distribution Type III 

Type III distribution is commonly known as a “bat-wing”. This distribution type is used to provide a larger area of lighting from a position along the perimeter of where lighting is required. At a lateral width of 40 degrees, light will project outward and is optimal for lighting areas with a width no more than 2.75 times the mounting height. It is typically used for driveways, garages, and even sports fields.

• IES Distribution Type IV 

Type IV has a lateral width of 60 degrees and is known as a “forward throw” distribution. It is the distribution type to choose if you are looking to illuminate sides of building facades, walls or parking areas. Much like Type III, it is best for areas up to 2.75 times the mounting height in width. 

• IES Distribution Type V 

Type V distributes a circular pattern (there is also a Type VS that produces a square distribution with a more defined angle). Having the same distribution at all lateral angles, it is perfect for general area lighting—the ideal choice if you are looking to do parking lots or intersections. 

The site geometry for your design plays an important role in selecting the best luminaire distributions. Understanding these IESNA outdoor lighting distribution types will help you decide what's best for your design.