NEMA 7x6 vs. 5x5: Selecting Beam Spreads for Wide Industrial Yards
In large-scale industrial yard lighting, the difference between a high-performance installation and a costly failure often comes down to the NEMA (National Electrical Manufacturers Association) beam spread classification. For facility managers and contractors, the decision between a NEMA 7x6 (wide) and a NEMA 5x5 (medium) distribution determines visibility for operators, total fixture count, pole height requirements, and long-term energy expenditure.
Quick Decision Card: Selecting Your Distribution
| Scenario | Recommended Beam | Primary Reason | Key Verification |
|---|---|---|---|
| Low Poles (<40ft) | NEMA 7x6 | Maximizes horizontal overlap to eliminate dark spots. | Check for "Batwing" candela plot. |
| High Mast (≥50ft) | NEMA 5x5 | Projects intensity further to maintain center-yard fc levels. | Shielding required for glare control. |
| Perimeter Lighting | Asymmetric (7x5) | Reduces light trespass on neighboring property. | Full-cutoff (90° tilt) mandatory. |
The Core Decision Rule: The selection rests on the Spacing-to-Mounting Height (S/MH) ratio. Failing to match the beam spread to the yard geometry typically results in "hot spots" directly under poles and dangerous dark zones in the center of the yard—a common pitfall that compromises safety and operational efficiency.
Decoding NEMA Beam Classifications
The NEMA beam spread system categorizes light distribution based on the angle at which the light intensity drops to 10% of its maximum value (the field angle). This is expressed as two numbers (Horizontal x Vertical), ranging from 1 (narrowest) to 7 (widest).
- NEMA 5 (Medium): 70° to 100° field angle.
- NEMA 6 (Wide): 100° to 130° field angle.
- NEMA 7 (Very Wide): 130° and greater.
A NEMA 7x6 fixture offers a very wide horizontal spread (over 130°) and a wide vertical spread (100°–130°). Conversely, a NEMA 5x5 fixture provides a more concentrated, symmetrical 70° to 100° beam in both directions.
The Significance of Photometric Verification
Relying solely on the NEMA classification is a frequent technical error. Two fixtures with an identical NEMA 7x6 rating can exhibit vastly different ground-level performance depending on their optical design. Professionals must verify performance using IES LM-79-19 reports. These reports, combined with .ies files, allow for accurate modeling in software like AGi32 or Visual Photometric Tool to ensure the target foot-candles (fc) are met across the entire site.
The Spacing-to-Mounting Height (S/MH) Logic
The most critical engineering metric for yard layout is the S/MH ratio. This ratio dictates how far apart poles can be placed while maintaining acceptable uniformity (typically an average-to-minimum ratio of less than 3:1).
NEMA 7x6: The Wide Wash Specialist
In wide industrial yards with mounting heights between 25 and 40 feet, a NEMA 7x6 spread is often the standard choice. Based on common site modeling for open-area lots, a NEMA 7x6 fixture typically supports a maximum S/MH ratio of approximately 1.5.
- Example: At a 30-foot mounting height, poles should be spaced no more than 45 feet apart (30ft x 1.5) to ensure overlapping light patterns.
NEMA 5x5: The High-Mast Contender
For larger yards requiring higher mounting heights (50 feet or more), a NEMA 5x5 beam becomes more effective. A NEMA 5x5 spread can often stretch to an S/MH ratio of ~2.0 in high-mast applications because the more concentrated beam maintains higher intensity at greater distances.
Parameter Boundaries for S/MH Recommendations
The recommended 1.5 and 2.0 ratios are heuristics based on the following standard assumptions:
- Target Illuminance: 1.0 to 3.0 average foot-candles (fc).
- Uniformity Goal: < 3:1 (Avg/Min).
- Ground Reflectance: 10% (Standard aged asphalt/concrete).
- Fixture Tilt: 0° to 15° (Higher tilts require narrower beams to prevent glare).
Pole Economics: Fixture Count vs. Infrastructure Cost
A common mistake in B2B procurement is focusing exclusively on the cost per fixture. In reality, the largest cost driver in outdoor lighting is the infrastructure—poles, concrete footings, and trenching.
The Taller Pole Trade-off
Choosing a NEMA 5x5 beam to increase spacing often necessitates taller poles. According to engineering samples from Lighting Analysts (AGi32), moving from a 40-foot pole to a 60-foot pole can triple the total installed cost per pole location. This is due to the exponential increase in wind load (EPA) requirements, which mandate significantly larger concrete footings and heavier gauge steel.
In many scenarios, a system using a higher count of NEMA 7x6 fixtures on shorter, 30-foot poles can result in a 15–25% lower total project cost. This estimate accounts for the savings in specialized heavy equipment (cranes) and the reduced cost of standard-duty poles.
Methodology Note: Cost Modeling (Estimated)
| Parameter | Low-Mount Strategy (NEMA 7x6) | High-Mast Strategy (NEMA 5x5) | Rationale |
|---|---|---|---|
| Mounting Height | 25–35 ft | 50–100 ft | Standard industrial vs. High-mast |
| Pole Unit Cost | $1,500 – $2,800 | $5,000 – $18,000+ | Material and foundation scale |
| Fixture Count | ~20% Higher | ~20% Lower | Based on 1.5 vs. 2.0 S/MH |
| Maintenance Access | Standard Scissor Lift | Specialized Crane/Bucket | Safety and equipment rental |
Case Study: Point-by-Point Modeling Example
To verify these heuristics, consider a 200ft x 200ft storage yard.
- Input: 200W LED Floodlight (28,000 Lumens), NEMA 7x6 distribution.
- Setup: 4 Poles (one at each corner), 30ft Height.
-
Simulation Output:
- Average Illuminance: 2.4 fc
- Minimum Illuminance: 0.8 fc
- Uniformity (Avg/Min): 3.0:1
- Conclusion: This layout meets the IES RP-7-17 recommendation for industrial parking/storage. If NEMA 5x5 fixtures were used at this height, the center of the yard would drop below 0.3 fc, creating a safety hazard.
Advanced Optics: Beyond the Symmetrical Beam
While 7x6 and 5x5 are foundational, modern yards benefit from asymmetric distributions. As noted in the 2026 Commercial & Industrial LED Lighting Outlook, asymmetric beams (e.g., NEMA 7x5) provide both width and forward projection.
The 'Batwing' Advantage
When reviewing .ies files, look for a "batwing" distribution in the candela plot. This indicates the fixture directs more light at angles between 45° and 60° rather than straight down (nadir). This distribution is highly effective for wide yards because it pushes light into the "black holes" between poles.
Full-Cutoff and Light Trespass
Industrial yards near residential zones must specify full-cutoff optics. These emit zero light above 90°. The DesignLights Consortium (DLC) QPL V5.1/V6.0 standards include specific requirements for glare and light trespass. Choosing a DLC Premium-listed fixture ensures the product meets these efficacy and distribution quality benchmarks.
Compliance and Regulatory Frameworks
- ASHRAE 90.1 & IECC 2024: These regulate Lighting Power Density (LPD). High-efficacy fixtures (130+ lm/W) are required to meet these wattage-per-square-foot limits.
- California Title 24, Part 6: Requires mandatory controls such as motion sensors. The California Energy Commission (CEC) specifies fixtures must be capable of dimming by at least 50% during unoccupied periods.
- UL 1598 & IP65 Ratings: Outdoor lighting must be UL 1598 listed for wet locations. An IP65 rating is the baseline for dust and water resistance.
Practical Layout Strategy: Perimeter vs. Center
The Hybrid Approach
- Perimeter Poles: Use NEMA 7x6 or asymmetric distributions with full-cutoff shielding to wash the yard without spilling light off-site.
- Interior Poles: If the yard requires interior poles, use NEMA 5x5 distributions at higher mounting heights to provide "fill" light for central aisles.
Verification Checklist for Contractors
- Request the LM-79 Report: Ensure lumens are verified by an independent lab.
- Check the TM-21 Projection: Verify long-term lumen maintenance. A 100,000-hour claim should be backed by IES TM-21 calculations.
- Run a Photometric Study: Use actual .ies files to confirm the S/MH ratio of 1.5 (for 7x6) or 2.0 (for 5x5) works for your yard.
Maximizing ROI with Utility Rebates
The financial viability of an upgrade often hinges on utility rebates. Most major U.S. utilities (e.g., PG&E, National Grid) require DLC Premium certification for the highest rebate tiers.
- Rebate Range: Depending on the utility territory and fixture wattage, rebates can offset 30–70% of the upfront fixture cost.
- Example: A $300 high-output floodlight may qualify for a $150–$200 prescriptive rebate in high-incentive regions like the Northeast or West Coast.
Tools like the DSIRE Database provide a look at local incentives. When calculating ROI, include energy savings (typically 65–80% over HID) and the elimination of maintenance cycles for 10+ years.
Choosing the Right Distribution for Your Yard
- Choose NEMA 7x6 for yards with mounting heights under 40 feet where horizontal width and high uniformity are the priorities.
- Choose NEMA 5x5 for high-mast applications (50ft+) or very narrow, long storage lanes where light needs to be projected over a distance.
For further guidance, refer to our technical guide on Designing a High Bay Layout for Warehouse Safety.
Disclaimer: This article is for informational purposes only and does not constitute professional engineering or electrical advice. Always consult with a licensed electrical contractor and local building authorities to ensure compliance with the National Electrical Code (NEC) and local ordinances.
Sources
- DesignLights Consortium (DLC) Qualified Products List
- IES LM-79-19: Optical and Electrical Measurements of SSL Products
- ASHRAE Standard 90.1-2022: Energy Standard for Buildings
- DSIRE: Database of State Incentives for Renewables & Efficiency
- Lighting Analysts: AGi32 Photometric Software Documentation