Type III vs Type V Light Distribution: Choosing the Right Optics
Understand IESNA light distribution types for outdoor LED fixtures. Compare Type II, III, IV, and V patterns for parking lots, streets, and building perimeters.
Light distribution type is one of the most important — and most overlooked — specifications when selecting outdoor LED fixtures. The wrong distribution wastes light and creates dark spots.
IESNA Distribution Types Explained
The Illuminating Engineering Society of North America (IESNA) classifies outdoor light distribution into five types:
| Type | Pattern | Throw | Best Application |
|---|---|---|---|
| Type I | Narrow, bilateral | 1× mounting height | Walkways, narrow pathways |
| Type II | Wider, bilateral | 1.5× mounting height | Narrow roadways, sidewalks |
| Type III | Medium forward throw | 2.75× mounting height | Parking lots, wide roads |
| Type IV | Semi-circular forward | 2.75× mounting height | Building perimeters, property lines |
| Type V | Circular/square | Equal all directions | Center-of-area, intersections |
Type III: The Parking Lot Standard
Type III distribution throws light forward and slightly to the sides, creating a rectangular pattern. It's the most versatile and widely used distribution for:
- Parking lots (perimeter and interior poles)
- Roadways and streets
- Large commercial areas
- Sports courts and fields
Auvolar's Area Light OT Series and PLB Series come standard with Type III distribution, optimized for parking lot applications.
Type V: The Circular Pattern
Type V distribution sends light equally in all directions, creating a circular or square pattern. Best for:
- Center-of-area poles (parking lot islands)
- Intersections and roundabouts
- Plaza and courtyard center lights
- Any pole not near an edge
When to Mix Distribution Types
Most parking lots benefit from a combination:
- Perimeter poles: Type III (throw light inward)
- Interior poles: Type V (throw light in all directions)
- Property line poles: Type IV (throw light onto property, not onto neighbors)
This mixed approach reduces the number of poles needed while maintaining uniformity.
Impact on Fixture Count and Cost
For a 200-space parking lot (80,000 sq ft):
| Layout Approach | Fixtures Needed | Cost (Auvolar 200W) |
|---|---|---|
| All Type III, perimeter only | 24 | $4,536 |
| Mixed Type III + V | 18 | $3,402 |
| All Type V, grid pattern | 20 | $3,780 |
The mixed approach typically requires the fewest fixtures while achieving the best uniformity.
How to Read a Photometric Report
Request IES files from Auvolar for any fixture. Import into AGi32 or DIALux to see:
- Iso-footcandle lines: Shows exactly where light falls
- Uniformity ratio: Should be 4:1 or better for parking lots
- Max/min ratio: Indicates hot spots and dark patches
Auvolar provides free photometric layouts for any project. Send us your site plan and we'll specify the optimal distribution type for each pole location.
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