Why Distribution Type Is a Property-Line Compliance Decision
In parking lot lighting, most “light pollution” problems are not caused by excessive lumens. They are caused by selecting the wrong distribution pattern for the pole location and site geometry. A fixture can meet target foot-candle levels and still create neighbor complaints if the optic sends light toward windows, property lines, or sky-facing angles.
Type III and Type V are common distribution patterns for area lights. Understanding how each throws light is the difference between keeping illumination on the pavement and pushing it into adjacent properties.
What Type III and Type V Distributions Actually Mean
IES distribution “types” describe how light is distributed across the ground plane. The practical takeaway is simple: Type III is forward-throw biased, while Type V is radially symmetric.
| Distribution | Pattern Description | Typical Use |
|---|---|---|
| Type III | Forward throw with limited backlight | Perimeter and edge-of-lot poles |
| Type V | Circular / symmetric distribution | Interior poles, open areas |
Choosing Type V on an edge pole is a common cause of light trespass because half of its output is inherently aimed outside the lot boundary.
How Optic Selection Controls Light Trespass
Light trespass is primarily about directionality at the property edge. The same total lumens can either stay on pavement or spill into adjacent parcels depending on the optic.
| Trespass Driver | How It Happens | Optic-Based Fix |
|---|---|---|
| Backlight at lot edge | Light projects behind pole toward property line | Use Type III (or add house-side shielding) |
| High-angle light | Light emitted near horizontal increases glare and window impact | Select optics with better glare control and cutoff |
| Over-tilt | Fixture aimed outward to “reach” dark areas | Correct spacing/height; avoid tilt as a correction method |
In practice, the safest approach for edge poles is a distribution that intentionally biases output inward.
Pole Placement Decides the Correct Distribution
Distribution type is not a preference—it is a response to where the pole sits relative to the area needing light.
| Pole Location | Best Distribution | Reason |
|---|---|---|
| Perimeter pole (along property line) | Type III | Keeps throw forward into the site |
| Corner pole | Type III + shielding (often) | Corners are the highest trespass risk points |
| Interior pole | Type V | Even radial coverage reduces scallops and dark pockets |
If poles cannot be moved, optic selection and shielding become the primary compliance tools.
Practical Layout Examples: Edge Poles vs. Interior Poles
Use Type III where you need controlled forward throw into the lot, particularly near residential boundaries or windows. Use Type V where poles are surrounded by pavement and you need uniformity in all directions.
- Retail lot with perimeter poles only: Type III is typically required to keep light inside the boundary.
- Large open lot with interior grid poles: Type V improves uniformity and reduces “striping.”
- Lots adjacent to residences: Prioritize low backlight optics, shielding, and reduced tilt.
When a lot is close to neighboring windows, the correct solution is almost never “more lumens.” It is better distribution and better glare control.
Dark Sky and Trespass Metrics to Check
To prevent violations and complaints, review these items during submittal and layout review:
| Check Item | What You’re Confirming | Why It Matters |
|---|---|---|
| Property-line spill light | Light levels at boundary are controlled | Limits trespass onto neighbors |
| Backlight control | Optic reduces emission behind pole | Protects windows and side yards |
| Uplight control | Minimal upward emission | Reduces sky glow and dark-sky conflicts |
| Glare control | Lower high-angle brightness | Reduces disability glare and complaints |
Distribution type should be reviewed together with shielding, aiming angle, and mounting height.
Common Optical Mistakes That Cause Violations
- Using Type V on perimeter poles along a property line
- Tilting fixtures to “reach” areas caused by incorrect spacing or height
- Ignoring backlight control and relying on “lower wattage” as a fix
- Skipping house-side shields near residential boundaries
- Equating average foot-candles with compliance
Most violations are preventable by matching distribution to pole placement and verifying boundary performance.
Related Outdoor Lighting Categories
Type III distribution is the default choice for perimeter poles because it pushes light into the site. Type V distribution belongs on interior poles where circular coverage improves uniformity without pushing light toward neighboring windows.
Brandon Waldrop
As the lead technical specialist for our commercial lighting technical operations, Brandon Waldrop brings over 20 years of industry experience in product specification, outside sales, and industrial lighting applications.
His career began in physical lighting showrooms, where he focused on hands-on product performance and technical support. He later transitioned into commercial outside sales, working directly with architects, electrical contractors, and facility managers to translate complex lighting requirements into energy-efficient, code-compliant solutions.
Today, Brandon applies that industry experience to architect high-performance digital catalogs and technical content systems, helping commercial partners streamline the specification process and deploy lighting solutions with total technical confidence.
