When designing outdoor and street lighting, understanding light distribution is critical to achieving safety, efficiency, and visual comfort. The Illuminating Engineering Society of North America (IESNA) defines several standardized distribution types—T1, T2, T3, T4, and T5—that describe how light spreads from a luminaire onto a surface. These classifications guide engineers, architects, and lighting manufacturers in selecting the most appropriate LED lens design for specific applications.
Follow this article to learn about the light distribution characteristics and corresponding application scenarios of Asahi's T1, T2, T3, T4, and T5 products.
T1 – Narrow Beam Distribution
Type I (T1) provides a very narrow, elongated light pattern, suitable for walkways, bike paths, and narrow corridors. The maximum intensity extends along the path with minimal spread, reducing light spill outside the target zone.
Lens design note: A narrow-beam LED lens design ensures controlled illumination with minimal glare.
T2 – Medium Narrow Road Distribution
Type II (T2) produces a slightly wider distribution compared to T1, creating an elliptical light pattern that is ideal for residential streets and side roads. The light extends outward but keeps most of the intensity directed toward the roadway.
Best Applications: Narrow to medium-width roads with side-mounted light poles. Asahi offers a variety of T2M and T2M-cutoff lens modules. Precise optical control helps minimize light waste while ensuring road safety.
T3 – Roadway and Parking Lot Distribution
Type III (T3) offers a wider spread of light, pushing illumination farther forward and sideways. This is one of the most common distributions for street and area lighting because it balances efficiency and coverage.
Lens design note: T3 distributions often use multi-lens arrays to achieve balanced forward throw and lateral spread.
T4 – Large Outdoor Area Distribution
Type IV (T4), also known as a forward throw distribution, directs light in a semicircular pattern. It throws illumination farther forward compared to T3 and is excellent for large areas or building perimeters.
Best application: Large outdoor spaces, sports fields, and wall-mounted fixtures for perimeter lighting.With precise LED lens design, T4 optics minimize light trespass into unwanted zones while ensuring uniform brightness.
T5 – Symmetrical Distribution
Type V (T5) produces a circular, symmetrical light pattern that spreads evenly in all directions. This type is highly effective when fixtures are mounted in central positions and illumination is required around the full perimeter.
Best application: Parking lots, plazas, and open public areas.Asahi’s optical engineering ensures even illumination without hot spots or dark zones.
The IESNA-defined light distribution types (T1, T2, T3, T4, and T5) provide a universal framework for designing outdoor and roadway lighting. Each type serves a unique purpose, from narrow pedestrian pathways to wide-open plazas.
By leveraging advanced LED lens design, manufacturers like Asahi lens deliver solutions that meet these distribution standards while optimizing energy efficiency, minimizing glare, and enhancing visual comfort.