Replacing T8/T5HO: UFO or Linear High Bay Fixture?

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.

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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:

• Cut energy and maintenance cost (kWh, lamp/ballast changes)
• Improve illuminance and uniformity at task level
• Meet current energy codes and qualify for rebates
• Simplify controls (0–10 V dimming, occupancy/daylight sensors)
• Reduce operational headaches (flicker, failed ballasts, color shift)

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. That is the economic engine behind most T8/T5HO retrofits.

Keep that 40–60% range in mind; your UFO vs linear decision should never sacrifice that level of savings.

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2. How UFO and Linear High Bays Actually Compare

Both UFO and linear LED high bays can replace T8/T5HO systems. The main differences show up in beam shape, layout flexibility, glare, and installation.

2.1 Quick Comparison Table

Use this table as a first filter before diving into specifics:

Factor	UFO High Bay	Linear High Bay
Typical mounting height	16–60 ft (5–18 m)	16–50 ft (5–15 m)
Best-fit spaces	Open areas, high clear heights, mixed-use	Aisles, racking, long narrow bays
Beam character	Symmetric, round distribution	Rectangular, aisle or wide distribution
S/H ratio (spacing / mounting height)	~1.0–1.5	~0.8–1.3 along aisles
Glare management	Needs reflectors/diffusers for low UGR	Easier to shield from view angles
Sensor integration	Often uses remote or hook‑mount sensors	Often has integrated aisle sensors
Install complexity	Fast hook/chain retrofit over old rows	Slightly more alignment work on rows
First cost	Often slightly lower per lumen	Often slightly higher, but fewer fixtures in aisles

The spacing-to-mounting-height (S/H) ranges above come from typical photometric layouts and are consistent with the maintained illuminance guidance in ANSI/IES RP‑7 for industrial facilities. For critical tasks, staying near S/H ≈ 1.0 helps maintain uniformity and target foot‑candles over time.

2.2 Light Distribution vs Your Space Geometry

UFO distribution

• Round, symmetric beam (typically 90–120°)
• Works best in open areas: clear floor plates, large workbays, gym-style spaces
• Good choice when you need flexibility and may rearrange equipment frequently

Linear distribution

• Rectangular patterns, often with aisle or narrow‑beam optics
• Ideal for pallet racking, long process lines, and narrow aisles
• Helps push light down between racks and across shelf faces, improving vertical illuminance

Practitioner experience shows a consistent pattern: where T8/T5HO strips were originally spaced down the center of aisles, linear LED high bays can often re‑use the same rows and achieve 10–20% better vertical uniformity than swapping to UFOs in the same locations. That extra vertical light matters for reading labels and barcodes at height.

2.3 Efficiency, LM79, and DLC Rebate Readiness

Whether you choose UFO or linear, a professional retrofit treats performance data and rebates as non‑negotiable.

• LM-79 photometric report: Confirms lumens, watts, efficacy (lm/W), CCT, CRI, and power factor using standardized test methods from the IES LM‑79‑19 standard. This is your performance “scorecard.”
• LM-80 + TM-21 lifetime: Shows LED package lumen maintenance testing and extrapolated L70 life, per IES LM‑80‑21 and TM‑21‑21.
• DLC listing: The DesignLights Consortium’s Qualified Products List is what most utility programs use to determine eligibility and incentive levels.

From multiple retrofit projects, an effective rule of thumb is:

• Target ≥130–150 lm/W (lumens per watt) for high bays replacing T8/T5HO.
• Require LM‑79 files and .ies photometry for every SKUs.
• Prefer fixtures already on the DLC QPL; rebates often add $25–$80 per fixture in many programs.

Any fixture that cannot provide LM‑79, LM‑80/TM‑21, and a DLC listing adds friction to your project approval and should be treated as a red flag.

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3. Converting T8/T5HO Performance Into High Bay Requirements

A practical decision framework starts with your existing fluorescent system. The goal is to match or improve maintained illuminance (foot‑candles or lux), not just “rated lumens on paper.”

3.1 Establish Your Baseline

For a typical T8/T5HO high‑bay fluorescent system:

• Mounting heights: 16–30 ft in small warehouses and shops; up to 40 ft in larger facilities
• Common layouts: 4‑ or 6‑lamp T5HO strips, or 4‑lamp T8 strips on 8–12 ft spacing
• Input power: ~220–320 W per 6‑lamp T5HO, ~128–192 W per 4‑lamp T8 row

Use a light meter to measure actual foot‑candles at:

• Floor level (for storage and walking safety)
• Workplane (usually 30–36 in above floor for benches and task areas)

Experienced designers typically assume a maintenance factor of 0.7–0.8 to account for dust, dirt, lumen depreciation, and surface aging. In practice, that means:

If you want 30 fc maintained, design the new LED layout for around 38–43 fc initial.

This aligns with the “initial vs maintained” illuminance approach described in ANSI/IES RP‑7 for industrial facilities.

3.2 Translate to UFO or Linear High Bays

Once you know your baseline and target maintained foot‑candles, use fixture photometry to size the retrofit.

Our field layouts show that replacing a 6‑lamp T5HO high‑bay (250–300 W input) with a 150–200 W LED high bay at ~140 lm/W typically:

• Cuts fixture power by 30–45%
• Maintains or improves horizontal illuminance by 10–20%, assuming similar spacing and mounting height

A few patterns emerge:

• At 16–24 ft mounting heights, linear high bays spaced at S/H ≈ 1.0–1.2 along aisles deliver very consistent aisle lighting.
• At 24–35 ft and above, UFO high bays become efficient, especially for open areas where row alignment is less important.

If your existing T8/T5HO layout already aligns over aisles, linear LED high bays can often drop into roughly the same row spacing with minor tweaks. UFOs may need denser spacing or careful aiming to avoid dark faces on high racks.

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4. Energy Codes, Controls, and Sensor Readiness

Fluorescent-to-LED retrofits now live in a stricter code environment than when those original T8/T5HO systems were installed.

4.1 Why 0–10 V Dimming and Sensors Are No Longer Optional

Modern codes and standards push two things:

• High efficacy (lm/W)
• Automatic controls (occupancy and daylight)

The ASHRAE/IES Standard 90.1‑2022 and the 2024 IECC commercial energy code both tighten lighting power density limits and expand mandatory controls for warehouses, open offices, and other large spaces. California’s Title 24, Part 6 adds even more prescriptive control requirements.

Across multiple retrofit projects, one consistent ROI pattern appears:

• Adding occupancy sensors and 0–10 V dimming in high‑bay spaces often yields an additional 20–30% energy savings over a basic LED‑only upgrade.
• Many utility programs pay extra incentives for fixtures that are sensor‑ready (integral sensor ports or leads) or shipped with controls installed.

This is why it is good practice to always specify high bays with 0–10 V dimming and sensor compatibility, whether UFO or linear.

4.2 UFO vs Linear: Controls Integration

Both UFO and linear high bays can support controls, but there are practical differences:

• UFO high bays

  • Often use external plug‑in or hook‑mount occupancy/daylight sensors.
  • Simple for open areas and grid layouts.
  • May require careful sensor selection at higher mounting heights (30+ ft) to ensure reliable detection.

• Linear high bays

  • Frequently offer integrated aisle sensors aligned with the beam pattern.
  • Work very well in long racking aisles, as the sensor field of view matches the aisle direction.

The U.S. DOE’s guide on wireless occupancy sensors for lighting controls in federal facilities notes that mounting height significantly affects sensor coverage and recommends matching sensor type and lens to the ceiling height and layout. This is especially important for high‑bay applications where the sensor might be 25–40 ft above the floor.

Pro Tip – Controls and Rebates

Utility programs typically require:

• DLC‑listed fixtures
• Documented connected load (watts)
• A documented control strategy (e.g., high‑/low‑trim settings)

Including 0–10 V and sensor readiness in your fixture spec from the start avoids costly add‑ons or re‑submittals during rebate review.

For zoning and dimming strategy in UFO applications, see the dedicated guide on zoning UFO high bay dimming controls.

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5. Installation & Mounting: What Changes From T8/T5HO?

Fluorescent T8/T5HO high bays are typically long strip or basket fixtures, mounted by chains, pendants, or surface brackets. When you retrofit to LED, pay attention to three things: mounting style, voltage, and commissioning.

5.1 Mounting and Physical Constraints

UFO high bays

• Usually mount via hook, loop, or single‑point pendant.
• Ideal for replacing a bank of strips with fewer, higher‑output fixtures in open areas.
• Reduce installation time; a single fixture can replace multiple T8/T5HO rows.
• Watch for clearance around sprinklers, crane rails, or mechanical equipment.

Linear high bays

• Mount via chain, aircraft cable, or rigid conduit at two points.
• Naturally line up with aisles and racking; good when you must maintain existing row geometry.
• Installation takes a bit longer per fixture but often yields better visual comfort in narrow spaces.

Under the National Electrical Code as summarized in the NFPA 70 overview, all wiring must follow rules for conductor types, junction boxes, and support. When converting from fluorescent strips with internal ballasts to remote drivers or external junction boxes, make sure your installation details remain compliant with local code based on NFPA 70.

5.2 Voltage, EMI, and Safety Compliance

When you replace older fluorescent systems, check:

• Line voltage: Many larger facilities use 277 V or 347–480 V. Ensure your chosen fixtures match the supply or include appropriate step‑down gear.
• Safety listing: Look for UL or ETL listing to UL 1598 (luminaires) and UL 8750 (LED equipment), verifiable in the UL Product iQ database or Intertek’s ETL directory.
• EMI compliance: LED drivers should comply with FCC Part 15 for unintentional radiators to reduce interference risks in facilities with sensitive electronics.

These requirements apply equally to UFO and linear high bays; do not compromise safety for form factor.

5.3 Commissioning: Don’t Skip the Light Meter

After installation, always:

1. Use a light meter to confirm target foot‑candles on the floor and at key tasks.
2. Adjust 0–10 V trims to tune light levels; many layouts intentionally oversize wattage and dim down for additional savings.
3. Verify sensor coverage, time‑outs, and high/low setpoints.

A common mistake is to rely only on visual impression. In large high‑bay spaces, the human eye adapts quickly, and a layout that “looks bright” may still miss Illuminance targets for inspection or assembly areas. A quick meter survey ensures the retrofit truly beats the former T8/T5HO performance.

For more on layout techniques and safety‑driven design, see the guide on designing a high bay layout for warehouse safety.

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6. Application Scenarios: UFO vs Linear for Common T8/T5HO Retrofits

This section walks through the most common retrofit scenarios and suggests which form factor generally works better.

6.1 Open Warehouse or Manufacturing Floor (20–30 ft)

Existing: 6‑lamp T5HO high bays or multiple rows of 4‑lamp T8 strips, wide open floor, mixed pallet storage and staging.

Goal: Maintain 30–40 fc at floor and 50+ fc at workbenches, improve reliability, add occupancy control.

Recommendation:

• Use UFO high bays with wide distribution (90–120°) for open areas.
• Target S/H around 1.2–1.4.
• Add integral or hook‑mounted occupancy sensors in zoning groups.

Many mechanics and maintenance shops with 18–25 ft ceilings choose this path because UFO high bays simplify mounting and provide bright task lighting; for example, see how mechanics are using this in practice in the article on UFO high bays for mechanic task lighting.

6.2 Long Aisles With Tall Racking (25–40 ft)

Existing: Continuous rows of T5HO or T8 strips directly over aisles, often with noticeable scalloping on the floor and dark rack faces.

Goal: Boost vertical illuminance on rack faces for picking and inventory; meet stricter energy codes.

Recommendation:

• Use linear high bays with aisle optics.
• Mount directly over aisle centerlines or offset per photometric layout.
• Set S/H around 1.0 along the aisle; adjust cross‑aisle spacing to fill gaps.

Field comparisons show linear high bays often deliver 15–25% more light on vertical faces at the same wattage compared to UFOs placed in the same row locations, because their beam is shaped to push light down the aisle rather than spilling into unused overhead volume.

6.3 Mixed-Use Shop or Barn (14–20 ft)

Existing: Rows of T8 strips, relatively low ceilings, combination of vehicle bays, benches, and storage.

Goal: Get more punch on the floor, reduce lamp failures, and keep glare in check when looking up.

Recommendation:

• For open bay areas, UFO high bays at moderate wattages, possibly with reflectors to reduce high‑angle glare.
• Over benches or narrow work zones, consider linear high bays or linear shop lights to concentrate light on tasks.

In many workshops, combining a few high‑powered UFOs for general light with more targeted linear fixtures over benches produces the best balance of comfort and visibility.

6.4 High-Ceiling Specialty Spaces (Arenas, Hangars, Sports)

Existing: T5HO rows or metal halide high bays, mounting heights 30–60 ft.

Goal: High uniformity, high CRI where needed, and tight glare control.

Recommendation:

• UFO high bays with high efficacy and optional reflectors, carefully laid out via photometric software (.ies files are mandatory).
• Consider linear high bays only where there is consistent racking or directional seating.

At these heights, round distributions simplify aiming and give designers flexibility to meet target lux levels with fewer luminaires.

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7. Common Misconceptions and Expert Warnings

7.1 Myth: “UFOs Are Always Better Than Linear Because They’re Newer”

The form factor is not a performance guarantee.

• High‑quality linear high bays can easily match or exceed UFO efficacy.
• For aisles and tight racking, linear fixtures usually win on vertical illuminance and glare control.

Treat UFO vs linear as a geometry and photometrics decision, not a generational or branding issue.

7.2 Myth: “As Long as the Lumens Match, the Retrofit Will Work”

Matching nameplate lumens from your old T8/T5HO system is not enough.

• Fluorescents lose output over time and with dirt; LEDs do too, just more slowly.
• Without applying a maintenance factor (0.7–0.8) and checking layout uniformity, you risk installing a system that starts bright but ages below task requirements.

Always design to maintained foot‑candles using proper lumen maintenance data from LM‑80/TM‑21.

7.3 Expert Warning: Don’t Ignore Flicker and Glare

Professional forums and practitioner experience highlight two non‑obvious failure modes when replacing T8/T5HO:

1. Drivers with high flicker can cause discomfort in some users or interfere with high‑speed cameras.
2. Bare high‑output LED boards at relatively low mounting heights (15–20 ft) can produce harsh high‑angle glare.

Mitigation steps:

• Seek drivers with low flicker specifications when critical tasks or visual inspection are involved.
• Use diffusers, lenses, or reflectors (especially with UFOs) when workers are frequently looking up, such as around vehicle lifts or mezzanines.

For a deeper look at visual comfort considerations, see the specifier‑focused article on low‑UGR high bay lighting.

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8. Step-by-Step Decision Framework: UFO or Linear for Your Retrofit

Use this checklist to structure your T8/T5HO retrofit decision.

1. Document the space

   • Measure dimensions, mounting heights, and racking layouts.
   • Note task types (storage, picking, inspection, machining, sports, etc.).

2. Measure existing light levels

   • Floor and workplane foot‑candles at representative spots.
   • Identify areas that are over‑ or under‑lit.

3. Set performance targets

   • Use RP‑7 or project specs for target illuminance.
   • Apply a maintenance factor of 0.7–0.8.

4. Pre‑select fixture type

   • Predominantly open areas or reconfigurable layouts → start with UFO.
   • Strong aisle/racking patterns → start with linear.
   • Mixed use → consider a combination.

5. Filter for compliance and rebates

   • Require LM‑79, LM‑80/TM‑21, and .ies files.
   • Verify DLC listing in the DLC QPL.
   • Confirm UL/ETL listing (UL 1598 / 8750) and FCC Part 15 compliance.

6. Plan controls from day one

   • Specify 0–10 V dimming and sensor‑ready fixtures.
   • Define zones and sensor types (aisle vs open area) early.

7. Run a photometric layout

   • Use IES files in a tool such as AGi32 or equivalent.
   • Test both UFO and linear options where the best choice is unclear.

8. Validate install details

   • Confirm mounting hardware, clearances, and voltage.
   • Ensure NEC‑compliant wiring and junction box strategy.

9. Commission, measure, and tune

   • Verify foot‑candles after installation.
   • Adjust dimming and sensors to hit energy and comfort targets.

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9. Wrapping Up: When to Choose UFO vs Linear in Fluorescent Retrofits

Replacing T8/T5HO with LED high bays is one of the most impactful upgrades a facility can make. In most projects, the choice between UFO and linear comes down to three questions:

• Space geometry: Open and flexible → UFO; aisle‑driven and racked → linear.
• Visual tasks: High vertical illuminance or tight glare control often favors linear; wide‑open multipurpose areas tend to favor UFO.
• Project constraints: Installation time, existing mounting patterns, and rebate rules may push one form factor ahead.

If you treat UFO vs linear not as an aesthetic preference but as a tool choice driven by photometrics, controls, and compliance, your retrofit will deliver the energy savings, safety, and visual quality that modern standards expect.

For more in‑depth design support, including lumen selection by ceiling height, see the dedicated warehouse lumens guide for UFO high bays.

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Frequently Asked Questions

Do I have to replace every T8/T5HO strip with a one‑for‑one LED fixture?

No. Because high‑efficacy LED high bays deliver far more lumens per watt than most older fluorescent systems, many retrofits reduce fixture counts while maintaining or improving light levels. Use a photometric layout and a light meter to confirm coverage instead of mirroring the old layout.

Are UFO high bays too harsh for 16–18 ft ceilings in a shop?

Not necessarily. At these heights, choose moderate wattages, wide beam angles, and consider reflectors or diffusers to soften glare. Linear fixtures or additional lower‑output units can fill in over specific tasks if needed.

Can I keep my existing occupancy sensors when I switch from fluorescent to LED?

Sometimes. Many older sensors work fine with LED loads, especially when they control entire circuits rather than individual fixtures. However, high‑bay LED retrofits increasingly rely on fixture‑integrated or wireless sensors for granular control. Always verify sensor rating, mounting height suitability, and compatibility with the new driver loads.

How do I know if a fixture qualifies for rebates?

Most commercial lighting rebates require the fixture to appear on the DesignLights Consortium Qualified Products List. Check the exact model number against the QPL, then confirm any control or networked lighting requirements in your local utility’s program documentation.

Is 5000K always better than 4000K for high bays?

No. Color temperature is an application choice. Around 4000 K often works well for mixed‑use warehouses and manufacturing, while 5000 K is common for sports, inspection, and detailed work where a cooler “daylight” appearance helps. When retrofitting, involve stakeholders early; sudden jumps from warm fluorescents to cool LED can feel jarring if not communicated.

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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 to verify that your design and installation meet applicable codes, standards, and project‑specific requirements.