Moving on from fluorescent lighting in a warehouse, plant, or large shop usually comes down to one decision: for your T8/T5HO retrofit, should you use round UFO high bay fixtures or linear high bay fixtures?
For facility managers and contractors, the right answer depends less on fashion and more on photometrics, controls, mounting, and compliance. This guide lays out a practical decision framework you can reuse on every project, supported by industry standards and field-verified data.
1. Start With the Retrofit Goal: What Problem Are You Actually Solving?
Before comparing UFO vs linear high bay fixtures, clarify what you are trying to improve over the existing T8 or T5HO fluorescent system.
In most retrofit projects, the real objectives fall into five buckets:
- Energy/Maintenance Optimization: Cutting kWh and eliminating the 18,000–30,000 hour lamp replacement cycle.
- Illuminance Uniformity: Improving vertical light on rack faces and horizontal light at tasks.
- Code Compliance: Meeting ASHRAE 90.1 or IECC requirements for rebates.
- Advanced Control: Integrating 0–10 V dimming and occupancy sensing.
- Visual Quality: Reducing flicker and improving Color Rendering Index (CRI).
According to the U.S. Department of Energy’s Solid-State Lighting guidance for commercial and industrial luminaires, moving from fluorescent to well-designed LED high bays typically reduces lighting energy by 40–60% when paired with controls.
2. How UFO and Linear High Bays Actually Compare
Both UFO and linear LED high bays can replace T8/T5HO systems, but their photometric performance varies significantly based on space geometry.
2.1 Technical Comparison Table
Use this engineering filter to narrow your selection:
| Factor | UFO High Bay | Linear High Bay |
|---|---|---|
| Optic Geometry | Symmetric (Circular) | Asymmetric/Rectangular (Aisle) |
| Typical S/H Ratio | 1.0–1.5 (per ANSI/IES RP-7-21) | 0.8–1.3 (Longitudinal) |
| Vertical Illuminance | Moderate (spills in open space) | High (optimized for rack faces) |
| UGR (Glare) Rating | Typically 22–28 (lower with reflectors) | Typically 19–25 (shielded optics) |
| Standard Mounting | Hook/Pendant (Single-point) | Chain/Aircraft Cable (Two-point) |
| Efficiency (lm/W) | 135–180 lm/W | 130–170 lm/W |
| Best Application | Open Bays, Hangars, Gyms | Racked Aisles, Assembly Lines |
The spacing-to-mounting-height (S/H) ranges above are consistent with the maintained illuminance guidance in ANSI/IES RP‑7-21, Section 6.4 (Industrial Lighting Layouts). For critical tasks, staying near S/H ≈ 1.0 helps maintain uniformity and target foot‑candles (fc) over time.
2.2 Efficiency, LM-79, and DLC Rebate Readiness
A professional retrofit treats performance data as non‑negotiable. Ensure your submittals include:
- LM-79 Photometric Report: Per IES LM‑79‑19, this confirms total luminous flux and efficacy. Check Section 8.0 for luminous distribution data to ensure it matches your layout needs.
- LM-80 + TM-21 Lifetime: Shows LED package lumen maintenance. Per IES TM‑21‑21, look for an L70 rating of ≥50,000 to 100,000 hours.
- DLC Listing: Verify models on the DLC Qualified Products List. Rebates typically range from $25–$80 per fixture, often requiring DLC Premium status for maximum incentive.
3. Converting T8/T5HO Performance Into High Bay Requirements
The goal is to match or improve maintained illuminance, not just "rated lumens."
3.1 Establish Your Baseline (The 0.7–0.8 Rule)
For a typical T8/T5HO system, designers assume a Light Loss Factor (LLF) or Maintenance Factor of 0.7–0.8 to account for Lamp Lumen Depreciation (LLD) and Luminaire Dirt Depreciation (LDD).
Design Calculation:
Target Maintained fc / LLF = Required Initial fc Example: 30 fc (Maintained) / 0.75 (LLF) = 40 fc (Initial Design Target)
This aligns with ANSI/IES RP‑7-21 Table 6-1, which recommends specific illuminance targets based on task age and difficulty.
3.2 Field Data: T5HO vs. LED Retrofit (Case Study)
To validate the performance shift, consider this data from a recent 30,000 sq. ft. warehouse retrofit (25 ft mounting height):
| Metric | Original (6-Lamp T5HO) | Retrofit (150W Linear LED) | Change (%) |
|---|---|---|---|
| System Watts/Fixt. | 318 W | 150 W | -52.8% |
| Avg. Floor fc | 24 fc | 32 fc | +33.3% |
| Avg. Vertical fc | 8 fc (at 10 ft) | 14 fc (at 10 ft) | +75.0% |
| Uniformity (Max/Min) | 4.2:1 | 2.1:1 | +50.0% (Better) |
Note: The linear LED utilized a 60°x90° aisle optic, significantly boosting vertical light on racks compared to the diffuse fluorescent output.
4. Energy Codes, Controls, and Sensor Readiness
Modern retrofits must comply with ASHRAE 90.1-2022, Section 9.4.1.1, which mandates automatic lighting shutoff and occupancy-based reduction.
4.1 UFO vs. Linear: Controls Integration
- UFO High Bays: Best for Zonal Control. Often use plug-and-play microwave or PIR sensors.
- Linear High Bays: Best for Aisle-Specific Control. Integral sensors can be programmed with a "High/Low" trim (e.g., 100% when occupied, 20% when vacant) to maintain safety while maximizing savings.
The U.S. DOE’s guide on wireless occupancy sensors notes that mounting height significantly affects sensor coverage. For heights >30 ft, ensure the sensor lens is rated for "High Bay" detection to avoid "dead zones."
5. Installation & Compliance: NEC and UL Standards
5.1 Mounting Safety (NFPA 70 / NEC)
When converting from fluorescent strips, all wiring must follow National Electrical Code (NEC) Article 410 (Luminaires).
- Article 410.30(B): Requires specific support for luminaires. UFOs using a single hook must have a secondary safety cable if required by local jurisdiction or in high-vibration environments.
- EMI Compliance: Ensure drivers meet FCC Part 15, Class A to prevent interference with warehouse RF scanners or WiFi systems.
5.2 Safety Listings
Verify fixtures in the UL Product iQ database or Intertek’s ETL directory. Look for UL 1598 (Standard for Luminaires) and UL 8750 (LED Equipment for Use in Lighting Products).
6. Practitioner’s Toolkit: Field Survey & Calculation Template
Use this template to standardize your site audits.
A. Site Audit Checklist
- [ ] Ceiling Height: ________ ft
- [ ] Fixture Spacing (Existing): ________ ft (on center)
- [ ] Voltage: [ ] 120-277V [ ] 347V [ ] 480V
- [ ] Obstructions: (Sprinklers, HVAC, Cranes) ________________
B. Quick ROI Estimator (Simplified)
- Current kWh/year: (Total Watts / 1000) × Hours/Year = _______ kWh
- Proposed kWh/year: (Proposed Watts / 1000) × Hours/Year = _______ kWh
- Annual Savings: (Step 1 - Step 2) × Utility Rate ($/kWh) = $_______
- Estimated Rebate: Fixture Count × $_______ (per DLC QPL) = $_______
7. Common Misconceptions and Expert Warnings
7.1 Myth: “Lumen-for-Lumen is the Best Way to Spec”
Reality: Fluorescent fixtures are multi-directional; much of their light is trapped in the reflector (luminaire efficiency). LEDs are directional. A 20,000-lumen LED high bay often provides more "delivered lumens" to the workplane than a 24,000-lumen T5HO system.
7.2 Expert Warning: Flicker and Visual Fatigue
In manufacturing environments, high-flicker drivers can cause a stroboscopic effect on rotating machinery. Always specify "Flicker-Free" drivers (Percent Flicker <10% per IEEE 1789 standards) for safety and comfort.
For a deeper look at visual comfort, see the specifier‑focused article on low‑UGR high bay lighting.
8. Wrapping Up: The Final Decision Matrix
| If your space has... | Recommended Choice | Key Reason |
|---|---|---|
| Open floor, high ceilings (>30 ft) | UFO High Bay | High punch, simple installation. |
| Narrow aisles, tall racking | Linear High Bay | Optimized vertical fc on rack faces. |
| Low ceilings (<18 ft), high glare risk | Linear (with Lens) | Lower surface brightness, better comfort. |
| Frequent layout changes | UFO High Bay | Symmetric beam covers shifts in floor use. |
For more in‑depth design support, see the warehouse lumens guide for UFO high bays.
Frequently Asked Questions
Do I have to replace every T8/T5HO strip one‑for‑one?
No. Because LED efficiency is higher, you can often increase spacing or reduce fixture counts. Always validate with a photometric layout (.ies file analysis).
Can I keep my existing occupancy sensors?
Only if they are rated for the inrush current of LED drivers. Many older fluorescent sensors will fail prematurely or "weld" shut when used with high-wattage LED loads.
Is 5000K always better than 4000K?
No. 4000K is often preferred for long-shift manufacturing to reduce eye strain, while 5000K is standard for high-detail inspection and cold storage.
Disclaimer: This article provides general technical guidance on lighting retrofits and does not replace professional engineering, electrical, or safety advice. Always consult qualified engineers, electricians, and local authorities having jurisdiction (AHJ) to verify that your design and installation meet applicable codes (NEC, NFPA) and project‑specific requirements.