If you’re lighting a production floor to 50–100 footcandles, you need spacing you can trust before you open DIALux or AGi32. This guide turns “UFO 12 high bay spacing” into a repeatable workflow: a clear SC/SMH explanation, practical rules of thumb, mountingheight spacing charts for 120° optics across 12k/18k/24k lumen packages, and a worked lumenmethod example you can copy.
UFO 12 high bay spacing: SC vs SMH explained
Spacing Criterion (SC) is a property of a luminaire derived from its photometry. It represents the maximum spacingtomountingheight ratio that still maintains acceptable uniformity (simplified: where the midpoint between fixtures is about as bright as directly under a fixture). Designers apply it using the spacingtomountingheight ratio, SMH (also written S/MH or SHR):
Spacing (ft) = SMH × Mounting Height (ft)
For widebeam high bays around 120°, industry practice clusters in these starting bands:
Standard uniform layout (costeffective): SMH ≈ 1.25–1.5
Highuniformity layout (tighter min/avg): SMH ≈ 1.0–1.2
These bands align with practitioner guidance and examples that explain how SC translates into workable spacings for high bays. For a concise refresher with examples, see the PacLights Learning Center’s explainer on spacing and SC/SMH in high bays, which illustrates how ratios like 1.2–1.5 are applied in real layouts in their article How to Space High Bay Light Fixtures for Optimal Illumination.
Always remember: SMH is a starting point. Final spacing should be validated against the product’s actual SC from its IES file and checked for uniformity goals.
Manufacturing targets: designing for 50–100 footcandles
General manufacturing, assembly, and machine work commonly target a maintained average of 50–100 fc. Multiple credible industry resources present this band as typical design practice for productivity and visual comfort (OSHA minima are lower and not design targets). For context, see the econolight factory lighting overview discussing 50–100 fc ranges for manufacturing tasks and the FES Lighting explanation of OSHA minimums vs. design targets.
Use these ranges to select lumen packages and to size counts with the lumen method, then verify with pointbypoint calculations.
Standard uniform vs highuniformity layouts
Standard uniform (SMH 1.25–1.5): Prioritizes coverage and fixture efficiency. Expect wider spacing and fewer fixtures. Suitable for general production areas where an avg/min ratio around 3:1 is acceptable after verification.
Highuniformity (SMH 1.0–1.2): Reduces scalloping and tightens min/avg, improving visual consistency around machines and workcells. Spacing shrinks and fixture counts increase. Many teams apply this in inspection zones or visually critical areas.
Think of SMH like a dimmer on uniformity: turning it down (toward 1.0) smooths the lighting but “costs” you more fixtures.
UFO 12 high bay spacing charts by mounting height (120° optics; 12k/18k/24k lm)
Use the tables below to pick an initial grid. “Standard” uses SMH within 1.25–1.5; “HighUniformity” uses SMH within 1.0–1.2. Start in the middle of each band, then nudge tighter or wider as photometry dictates.
Note on optics: The spacing below assumes a wide 120degree distribution. If your specific luminaire uses a different optic (e.g., 90° medium), verify with its IES file and adjust SMH accordingly.
Spacing for 12,000lumen UFO (120°)
|
Mounting Height (ft) |
Standard Uniform Spacing (ft) |
HighUniformity Spacing (ft) |
|
12 |
15–18 |
12–14 |
|
16 |
20–24 |
16–19 |
|
20 |
25–30 |
20–24 |
|
24 |
30–36 |
24–29 |
|
26 |
33–39 |
26–31 |
Spacing for 18,000lumen UFO (120°)
|
Mounting Height (ft) |
Standard Uniform Spacing (ft) |
HighUniformity Spacing (ft) |
|
16 |
20–24 |
16–19 |
|
20 |
25–30 |
20–24 |
|
22 |
28–33 |
22–26 |
|
24 |
30–36 |
24–29 |
|
26 |
33–39 |
26–31 |
Spacing for 24,000lumen UFO (120°)
|
Mounting Height (ft) |
Standard Uniform Spacing (ft) |
HighUniformity Spacing (ft) |
|
18 |
23–27 |
18–22 |
|
20 |
25–30 |
20–24 |
|
22 |
28–33 |
22–26 |
|
24 |
30–36 |
24–29 |
|
26 |
33–39 |
26–31 |
How these numbers were derived: We applied the SMH bands to each mounting height (e.g., at 20 ft, Standard ≈ 1.25–1.5 → 25–30 ft; HighUniformity ≈ 1.0–1.2 → 20–24 ft). Lumen package guidance helps you match output to height and target fc; ultimately, your pointbypoint should confirm average illuminance and uniformity.
Validation reminders:
Keep spacing ≤ SC × MH from the luminaire’s actual IES.
Check avg/min uniformity in software before procurement.
For an overview of why these SMH ranges are widely used and how they relate to SC, see the PacLights article LED High Bay Lighting: Optimize Your Spacing, which discusses the common “1.2–1.5× mounting height” rule of thumb used in highbay layouts.
From spacing to fixture count: the lumen method walkthrough
Once you sketch a grid, convert it into a fixture count and confirm it meets 50–100 fc. The lumen method remains the industry workhorse:
Formulas
Total lumens needed = Area (ft²) × Target fc
Number of fixtures (N) ≈ Total lumens × LLF ÷ (Lumens per fixture × CU)
Assumptions you can start with in clean industrial spaces:
CU (Coefficient of Utilization): 0.70–0.80 (actual CU comes from the luminaire’s IES file and depends on room index and reflectances)
LLF (Light Loss Factor): ≈0.80 (typical LED LLD × LDD in clean plants; adjust per maintenance plan)
A solid reference on CU/LLF definitions and how they roll up into maintained illuminance is EleCalculator’s lighting calculations guide, which summarizes the method and factors used in standard practice.
Worked example (medium production bay)
Space: 100 ft × 120 ft = 12,000 ft²
Target: 70 fc maintained
Candidate luminaire: 18,000 lm (120°)
Assumptions: CU = 0.70, LLF = 0.80
Calculations:
Total lumens needed = 12,000 × 70 = 840,000 lm
Fixtures required N ≈ 840,000 × 0.80 ÷ (18,000 × 0.70)
N ≈ 672,000 ÷ 12,600 ≈ 53.3 → plan for 54 fixtures (round to a grid)
Nominal spacing from that count: Area per fixture ≈ 12,000/54 ≈ 222 ft²; square grid ≈ √222 ≈ 14.9 ft. That’s tighter than the Standard SMH range at, say, 20 ft mounting height (25–30 ft). Two levers to reconcile the difference:
Increase the lumen package (e.g., 24k lm), or
Reduce the target fc or accept highuniformity spacing (SMH 1.0–1.2) while confirming the average still hits 70 fc.
Disclosure and product note: In practice, you would do this with the actual product file. For example, you might select the JCE Lighting UFO 12 LED High Bay and request its IES to plug exact CU and SC values into the workflow. Disclosure: JCE Lighting is our product.
Sensitivity checks you should run in software:
CU ±0.1 can swing counts by double digits.
LLF shifts with maintenance/ambient dust. Model your real schedule.
When a 90degree optic makes more sense
Wide 120° optics spread light beautifully at modest mounting heights, but at taller ceilings (often above ~22–26 ft depending on targets), center illuminance can sag. A medium 90° optic concentrates light, helping maintain target fc from height and improving control over spill. For a balanced overview of beam selection for high bays in industrial spaces, see PEB International’s guide to high bay lights for industrial spaces discussing when narrower beams help at taller mounting heights.
Rule of thumb: if you find yourself tightening SMH below 1.0 just to hold target fc at height, evaluate a 90° distribution or a higheroutput package.
Common pitfalls and quick checks
Reflectances matter: Dark ceilings/walls push CU down. If you’re under CU 0.65, expect more fixtures than the tables imply.
Glare and visual comfort: Check UGR/Veiling luminance proxies around machines and glossy surfaces; add reflectors/diffusers if needed.
Obstructions: Cranes, ducts, and mezzanines can shadow the grid. Simulate with volumes or plan supplemental task lighting.
Maintenance reality: If cleaning is infrequent or ambient dust is high, lower LLF and resize counts.
Validate with photometry and plan your next steps
Here’s the deal: the charts and SMH bands get you 80% of the way, fast. To finish the job, request the product IES, run a pointbypoint, and confirm both average illuminance and uniformity against your target band (50–100 fc) and your visual goals. If you’re specifying the UFO 12, ask JCE Lighting support for IES files, confirm SC, and verify CU from the tables embedded in the photometric data: UFO 12 LED High Bay on jcelighting.com.
If your verification shows the grid drifting from the SMH bands above, adjust spacing or optic (120° vs 90°) and iterate once more. It’s a quick loop that prevents surprises on install day.
FAQ
How do I choose between SMH 1.3 and 1.5 for standard layouts?
Start at 1.3 when tasks are more precise or when darker finishes reduce CU; widen toward 1.5 in open, brighter areas where slight dips between fixtures aren’t a concern. Confirm spacing ≤ SC × MH from the product IES.
Which lumen package should I pick at 20–22 ft to hit ~70 fc?
Begin with 18k–24klumen options at 120° optics. If the lumenmethod estimate forces spacing well below the Standard SMH band, move up in lumens or tighten to the HighUniformity band and validate in software.
Do these tables guarantee compliance with 50–100 fc targets?
No. They are starting points. Final compliance requires the product IES, CU from photometric tables, LLF matching your maintenance plan, and a pointbypoint calculation. Use the charts to set expectations and speed up iteration.
Can I use these spacings for aisles and rack areas?
Aisles often need different optics or rowbased spacing to maintain uniformity down the aisle path. Treat open production bays and aisle lighting as separate layout problems and verify each with photometry.