North American Street Lighting Standards: IESNA Classifications

Overview of the IESNA Classification System

The Illuminating Engineering Society of North America (IESNA) created a classification system that defines how light is distributed across horizontal surfaces. This framework is essential for designing roadway, parking, and other outdoor lighting projects in North America, offering a common standard for describing luminaire performance.

The system evaluates light distribution by identifying where the majority of illumination falls on a standardized grid, with particular focus on peak and 50% candela intensity points. Both lateral (across the road) and vertical (along the roadway) distributions are considered. The comprehensive standard governing these applications is outlined in ANSI/IES RP-8 – Recommended Practice for Roadway and Parking Facility Lighting, which consolidates prior IES standards and covers design, energy efficiency, safety, and environmental concerns.

Lateral Light Distribution Categories

The IESNA system categorizes lateral light distribution into six main types—Type I, II, III, IV, V, and VS. These classifications are determined by the point where the luminaire achieves 50% of its maximum intensity.

Type I

Characteristics: Produces a narrow elliptical light pattern, with the primary beam around 15 degrees. The 50% candela points fall between one mounting height (MH) on the house side and one MH on the street side.
Applications: Ideal for sidewalks, narrow pathways, single-lane roads, and boundary lighting.

Type II

Characteristics: Creates a narrow asymmetrical pattern, about 25 degrees wide. The 50% candela points fall between one MH on the street side and 1.75 MH.
Applications: Well-suited for one- to two-lane roads, side streets, jogging trails, bike lanes, and wide sidewalks.

Type III

Characteristics: Provides a broader asymmetrical pattern with a lateral width of about 40 degrees. The 50% candela range extends between 1.75 MH and 2.75 MH.
Applications: Commonly used for major corridors, highways, parking lots, and larger outdoor areas requiring extended coverage.

Type IV

Characteristics: Delivers an asymmetrical forward-throw pattern with an approximate width of 60 degrees. The 50% candela range falls between 2.75 MH and 3.75 MH. It produces a semi-circular, forward-focused light, minimizing backward spill.
Applications: Suited for perimeters, plazas, parking areas, and building exteriors where forward-focused illumination and spill control are critical.

Type V

Characteristics: Emits a fully symmetrical circular light pattern, distributing uniform intensity in all directions.
Applications: Effective for central mounting in large open spaces such as parking lots, parks, intersections, and task areas.

Type VS

Characteristics: Similar to Type V but generates a square symmetrical pattern with uniform intensity at all angles.
Applications: Best for large open areas requiring square-shaped, even illumination such as parking lots and public squares.