What are the light distribution types for LED streetlights?
According to the IESNA (Illuminating Engineering Society of North America) classification, LED streetlight light distribution types are primarily categorized as follows:
Type I: Produces an elliptical light pattern that is narrow in the lateral direction (perpendicular to the road). It is suitable for narrow roads, sidewalks, and bicycle paths, with a mounting height of ≤8 meters.
Type II: Features moderate lateral expansion; suitable for one- or two-lane roads, with a mounting height of 8–10 meters.
Type III: Offers wider lateral coverage; suitable for two- to three-lane roads, with a mounting height of 10–12 meters. This is the most commonly used type.
Type IV: Provides very wide lateral coverage, resulting in a rectangular light pattern. It is suitable for wide roadways (four lanes or more), plazas, and intersections, with a mounting height of 12–15 meters. It often employs an asymmetric (offset) distribution to direct more light toward the area away from the pole.
Type V: Features a symmetrical circular or square light distribution; suitable for central plazas and roundabouts, providing uniform illumination in all directions.
Additionally, there are asymmetric and cut-off light distribution types, which are used to reduce glare and light pollution.
The selection of a light distribution type is based on road width (W), mounting height (H), and pole spacing (S). A rule of thumb is that the W/H ratio determines the appropriate distribution type: for example, a W/H ratio of 1.0 calls for Type II; 1.5 for Type III; and 2.0 for Type IV.
For LED streetlights, the light distribution type is typically adjusted by changing the lens. Manufacturers should provide IES files for each distribution type to enable designers to perform simulations. An incorrect choice of light distribution can lead to bright spots or dark areas on the road surface, resulting in poor uniformity.
