Why More Wattage Isn’t Always Better for High Bays
Many warehouse and garage projects still start with one question: “How many watts do I need?” That question often leads to over‑lit spaces, failed rebate applications, and higher utility bills than necessary. For UFO high bay lights, wattage is just the input. What actually matters is: delivered illuminance (footcandles or lux), lumens per watt (efficacy), optics, and controls.
This article walks through a practical framework to size UFO high bays by task, not by wattage, so you can hit target light levels, qualify for incentives, and avoid glare and wasted energy.
1. The Problem With “More Watts = Better Light”
1.1 Why wattage is a poor design metric
Wattage is simply electrical power draw. Two different high bays can both be 200 W and deliver completely different results:
- A low‑efficacy unit at 110 lm/W → ~22,000 lumens
- A high‑efficacy unit at 150 lm/W → ~30,000 lumens
That’s a 36% difference in light output for the same wattage. According to the U.S. Department of Energy’s FEMP high‑efficiency LED luminaire guidance, industrial and high‑bay luminaires commonly achieve well above 130 lm/W, and leading products exceed that baseline. If you size by watts alone, you don’t benefit from these gains.
From the field, three common issues show up when projects are specified by wattage instead of performance data:
- Over‑lighting: spaces end up with 80–100 footcandles (fc) where 20–30 fc would be adequate for general warehouse work.
- Failed or reduced rebates: many utility programs key off lumens and efficacy and reference the DesignLights Consortium (DLC) Qualified Products List. A “200 W high bay” that doesn’t meet DLC minimum efficacy may receive no incentive at all.
- Unnecessary electrical infrastructure: breakers, wiring, and panel capacity are sized for higher demand than needed.
1.2 What actually defines a good high bay design
A professional high bay layout is built around:
- Maintained illuminance at work plane (fc or lux), by task
- Lumen package and efficacy (lumens and lm/W)
- Optics (beam angle, distribution) matched to mounting height and space geometry
- Controls (0–10 V dimming, occupancy/daylight sensors) to trim energy use
Standards and best‑practice guides like ANSI/IES RP‑7 – Lighting Industrial Facilities define typical illuminance targets for industrial spaces. RP‑7 recommends higher light levels for precision assembly or inspection than for bulk storage; the goal is safe, efficient visual performance, not a specific wattage number.
2. Start With Illuminance Targets, Not Watts
2.1 Practical footcandle ranges by application
For most warehouse, shop, and garage projects, practical maintained illuminance targets look like this (summarizing common practice and aligning with ranges in ANSI/IES RP‑7):
| Space / Task Type | Typical Maintained Target (fc) | Notes |
|---|---|---|
| Bulk storage, aisles | 3–10 fc | Safety and wayfinding; higher end for mixed traffic with forklifts. |
| General warehouse / assembly | 20–50 fc | Typical for picking, packing, light assembly. |
| Automotive / farm shop | 30–60 fc | Supports under‑hood work and general repair. |
| Precision inspection, fine work | 50–100+ fc | Electronics repair, quality inspection benches. |
These are maintained values—after lumen depreciation and dirt. New installations should often be designed 10–20% higher initially to account for light loss over time, consistent with the lumen maintenance thinking behind IES LM‑80 and lifetime projections per IES TM‑21.
2.2 Converting illuminance to needed lumens
A simple planning relationship ties illuminance, lumens, and area together:
Required lumens ≈ Target fc × Area (sq ft) ÷ Light‑loss factor
If you allow a 0.8 light‑loss factor (20% depreciation and dirt):
- 5,000 sq ft general warehouse
- Target 30 fc maintained
Required initial lumens:
- 30 fc × 5,000 sq ft ÷ 0.8 ≈ 187,500 lumens
You then select fixtures and quantities that deliver this lumen total, factoring in optics and spacing.
2.3 Why surface reflectance matters
Dark ceilings, walls, and floors absorb light. In practice, projects with dark matte surfaces often need 10–30% more lumens to achieve the same footcandles on the floor as a white, reflective interior. IES RP‑7 discusses maintenance and surface conditions as part of the design process; ignoring them is one reason many “rule of thumb” wattage guesses miss the mark.
3. Efficacy and DLC: The Real Levers Behind Wattage
3.1 Understanding lumens per watt (lm/W)
Efficacy tells you how much light you get from each watt. For UFO high bays, practical bands look like this:
| Efficacy Band | Approx. Range (lm/W) | Typical Context |
|---|---|---|
| Outdated / low | 100–120 | Legacy LED, many non‑listed imports. |
| Standard commercial | 125–140 | Meets many basic specs, borderline for some rebates. |
| High‑performance value | 140–155 | Strong lm/W, often DLC Standard. |
| Premium efficiency | 155–170+ | Common for DLC Premium at high bay wattages. |
The DLC’s SSL Technical Requirements for high bays (referenced in their QPL) set minimum efficacy thresholds and additional criteria such as color quality and lumen maintenance. Products that meet DLC Premium generally sit in the upper bands above, providing more lumens per watt.
3.2 How efficacy changes the wattage you actually need
Let’s bring back the earlier 187,500‑lumen example and compare fixture choices:
- Option A – Lower efficacy: 22,000‑lumen high bay at 120 lm/W → ~183 W
- Option B – Higher efficacy: 28,000‑lumen high bay at 155 lm/W → ~180 W
To reach 187,500 lumens:
- Option A: 187,500 ÷ 22,000 ≈ 9 fixtures → 9 × 183 W ≈ 1,647 W
- Option B: 187,500 ÷ 28,000 ≈ 7 fixtures → 7 × 180 W ≈ 1,260 W
Both approaches deliver similar light levels, but the higher‑efficacy choice cuts system wattage by roughly 24%, while using fewer fixtures, drivers, and connections.
Utility rebate structures, as summarized in the DSIRE incentive database, typically pay per qualifying DLC fixture or per reduced watt relative to baseline. In many real projects, stepping up to higher‑efficacy, DLC‑listed luminaires reduces net installed cost once incentives and energy savings are modeled.
3.3 Why “oversizing for safety” backfires
It is common to see designs that “play it safe” by:
- Choosing the highest wattage available (e.g., 240 W) at every mounting point
- Packing fixtures at very tight spacing regardless of photometric data
Our project reviews consistently show side effects:
- Glare and complaints: operators report eye fatigue and difficulty looking up at product locations.
- Poor payback: even with rebates, the extra load stretches simple payback by several years compared with a right‑sized layout.
- Control under‑use: when spaces are over‑lit, people dim manually or install lower‑output lamps, wasting the investment in the actual fixtures.
A better approach is to right‑size lumen packages to the task, then keep some headroom by specifying 0–10 V dimming and sensor‑ready drivers, aligning with control concepts covered in NEMA’s LSD 64 lighting controls terminology guide. You design for the task, then control for the exceptions.
4. Beam Angle, Spacing, and Mounting Height: The Hidden “Wattage Multipliers”
4.1 Why optics often matter more than more watts
Optics determine where lumens go. A 150 W high bay with tight, well‑controlled optics at 160 lm/W can put more useful light on the floor than a 200 W bare‑lens unit spraying light in every direction.
Key optical choices for UFO high bays:
- Wide beam (100–120°): good for low to mid mounting heights and open areas.
- Medium beam (80–90°): better punch for 20–30 ft heights in aisles or task zones.
- Narrow beams (60° or less): specialized, used for very high mounting or focused tasks.
The spacing‑to‑mounting‑height ratio (S/MH) is a practical field heuristic:
- For uniformity with UFO high bays, target S/MH ≈ 0.8–1.2.
- For higher task illuminance, use 0.6–0.8 in the work zone.
If S/MH creeps up to 1.5 or more, you typically see “striped” lighting—bright under fixtures, dark in between—which leads people to bump wattage, when the real fix is tighter spacing or adjusted optics.
4.2 Using IES files instead of guessing
Professional layouts rely on photometric files (.ies) documented by IES LM‑63. Lighting design software such as AGi32 reads these files to simulate exact distributions.
A robust workflow:
- Obtain .ies files and LM‑79 photometric reports early in the quoting process.
- Model the space in AGi32 or similar.
- Adjust mounting height, beam angle, and S/MH first.
- Only increase wattage after these variables are optimized.
This is the standard approach in engineering‑driven projects, and it is the fastest route to DLC‑ and code‑compliant designs.
4.3 Example: 20 ft shop, 30 × 60 ft
Consider a mixed‑use automotive shop:
- 20 ft mounting height
- 30 × 60 ft (1,800 sq ft)
- Target 40 fc maintained (general work, occasional detail work)
Required lumens (LLF 0.8):
- 40 × 1,800 ÷ 0.8 ≈ 90,000 lumens
Two design options:
-
Option 1 – “More watts” mindset
Twelve 200 W high bays at 135 lm/W → 27,000 lm each
Total lumens ≈ 324,000, S/MH ≈ 15 ft spacing ÷ 20 ft height = 0.75
Result: ~140 fc average, serious glare, and almost 2.4× the needed light. -
Option 2 – Task‑based mindset
Eight high bays around 12,000–13,000 lm each (roughly 80–100 W at 140–150 lm/W)
Total lumens ≈ 100,000–104,000, similar S/MH, proper optics
Result: 40–50 fc average, plenty of punch on the vehicles, but comfortable and efficient.
Both shops “look bright,” but the first pays for extra power and wiring forever. The second hits the spec with a fraction of the load.
For more step‑by‑step layout thinking, see the complementary guide on designing a high bay layout for warehouse safety.
5. Controls: The Safety Valve for Right‑Sized Wattage
5.1 Why dimming and sensors beat oversizing
When owners insist on some extra brightness for flexibility, the safest way to provide it is controllable headroom, not brute‑force wattage.
Recommended control capabilities for modern high bays:
- 0–10 V continuous dimming down to at least 10% output
- Occupancy sensors (remote or integrated) for automatic setback in empty zones
- Daylight‑responsive control near dock doors, skylights, or open walls
Guides such as the U.S. DOE’s Wireless Occupancy Sensors for Lighting Controls application guide for federal facilities show that pairing LED luminaires with occupancy sensing in warehouses and similar spaces typically yields 30–60% additional energy savings beyond the upgrade from legacy sources. That reduction is on top of right‑sized wattage.
5.2 Code and standard drivers toward controllable high bays
Energy codes like ASHRAE 90.1‑2022 and IECC 2024 push projects in this direction by requiring:
- Multi‑level or continuous dimming in many commercial spaces
- Occupancy control in warehouses, storage rooms, and similar areas
- Daylight responsiveness in daylit zones
The ASHRAE standard’s commercial lighting chapters, summarized on its Standard 90.1 resource page, explicitly tie allowed lighting power density and control requirements together. Meeting these targets is much simpler if you start with high‑efficacy, controllable high bays instead of oversizing fixed‑output fixtures.
For projects in California, the Title 24 Part 6 framework and its 2022 lighting controls application resource go further, specifying occupied/unoccupied levels, sweep‑off timing, and functional testing. A slightly smaller, controllable high bay layout nearly always integrates more smoothly with those rules than an oversized, non‑dimmable design.
6. Simple Sizing Framework: From Tasks to Wattage
6.1 Quick decision table: luminosity and wattage by height
The following table illustrates a task‑based starting point for UFO high bays, assuming modern, high‑efficacy fixtures (roughly 140–160 lm/W) and typical S/MH ratios. It is not a substitute for a full photometric layout, but it aligns with the illuminance ranges discussed earlier.
| Mounting Height | Typical Use Case | Approx. Lumens per Fixture | Ballpark Wattage Range* | Typical Target fc |
|---|---|---|---|---|
| 12–16 ft | Small garage, hobby shop | 8,000–12,000 | 60–90 W | 20–40 fc |
| 16–20 ft | General warehouse, farm shop | 12,000–18,000 | 90–130 W | 25–45 fc |
| 20–26 ft | Warehouse aisles, auto repair bays | 18,000–24,000 | 120–170 W | 30–50 fc |
| 26–35 ft | Large warehouse, sports/practice | 24,000–30,000+ | 160–220 W | 30–60 fc |
*Assuming 140–160 lm/W efficacy. If your fixtures are less efficient, wattage rises for the same lumen package.
6.2 Step‑by‑step checklist
Use this practical checklist instead of a wattage guess:
-
Define tasks by area
Map storage, general work, and precision zones; assign target footcandle ranges from Section 2. -
Measure space and mounting height
Length, width, clear height to fixture bottom. -
Estimate total lumens by zone
Use lumens = target fc × area ÷ 0.8. -
Select efficacy band
Prefer fixtures at or above DLC thresholds (consult the DLC QPL) to maximize lm/W and rebate eligibility. -
Pick a lumen package
Choose fixtures whose lumens and beam angle suit your mounting height and S/MH target. -
Check layout with IES files
Import .ies files into AGi32 or similar; verify average fc, uniformity, and glare. -
Add controls headroom
Specify 0–10 V dimming and sensor‑ready fixtures; design control zones aligned with real use patterns. -
Cross‑check with code and incentives
Confirm that lighting power density and controls satisfy ASHRAE 90.1/IECC/Title 24 and that the luminaires appear on the DLC QPL for rebates.
Working this list end‑to‑end is the most reliable way to avoid paying for unnecessary watts.
7. Common Myths About High Bay Wattage
Myth 1: “You can’t have too much light in a warehouse.”
Reality: Excess light causes disability and discomfort glare, especially at higher mounting heights where luminaires are in the line of sight for forklift operators. Guidance on visual comfort in industrial spaces within documents like IES RP‑7 and NEMA glare white papers reinforces that more lumens are not always helpful; the aim is balanced luminance, not maximum lumens.
Myth 2: “Higher wattage fixtures always look brighter.”
Reality: Perceived brightness depends on illuminance at the task plane and contrast, not nameplate watts. A 150 W high‑efficacy high bay with good optics can make a workbench look brighter than a 240 W unit with poorly controlled distribution that wastes light on upper walls and ceiling.
Myth 3: “Rebates just care about watts reduced, so oversizing is fine.”
Reality: Most commercial and industrial programs filtered in the DSIRE database reference DLC listing, measure savings relative to code baselines, and cap incentives at a percentage of project cost. Oversized wattage reduces your savings relative to a right‑sized, high‑efficacy design and can push your lighting power density above what codes permit.
Myth 4: “Choosing by lumens is too complicated for small shops and garages.”
Reality: Once you know your square footage and ceiling height, the simple framework in Sections 2 and 6 is fast. For example, a 24 × 30 ft, 14 ft‑high garage targeting ~30 fc typically lands around four to six high‑efficacy UFO fixtures in the 8,000–10,000 lumen range, depending on reflectance and spacing. That can be calculated in minutes and avoids years of unnecessary energy cost.
For more garage‑specific lumen and layout ideas, see the dedicated warehouse lumens guide for UFO high bay lights.
8. Pro Tip: Verify Data Early to Avoid “Paper Watts”
A recurring problem in real projects is what many contractors call “paper watts” and “paper lumens” — numbers that appear in marketing bullets but are not backed by test data.
To avoid this trap:
- Ask for LM‑79 reports from accredited labs, based on IES LM‑79‑19. These reports provide independently measured input watts, lumens, CCT, CRI, and power factor for a specific luminaire.
- Request LM‑80/TM‑21 documentation for the LED packages. Combined, LM‑80 and TM‑21 show how lumen output holds up over time and support lifetime claims like “L70 at 60,000 hours.”
- Confirm safety and EMC compliance in UL or ETL directories and FCC Part 15 records. Safety listings (e.g., based on UL 1598 and UL 8750 scopes) and FCC Part 15 compliance protect you from inspection issues and radio‑frequency interference in sensitive facilities.
This documentation turns a wattage label into a verifiable performance specification and is increasingly required for bids, permitting, and channel partners.
9. Wrapping Up: Design to Footcandles, Let Wattage Follow
When high bays are chosen by wattage alone, projects tend to drift toward more fixtures, more energy, and more glare than the work actually requires. A task‑based approach flips that script:
- Start from maintained footcandles by task and your actual square footage.
- Translate that into required lumens, then choose high‑efficacy, DLC‑listed fixtures.
- Tune beam angle, S/MH, and controls before increasing wattage.
- Verify claims with LM‑79, LM‑80/TM‑21, UL/ETL, and FCC Part 15 documentation to keep specs honest.
For facility managers and contractors, this approach reduces energy spend, simplifies code and rebate compliance, and delivers brighter, safer, and more comfortable spaces—without paying for every extra watt.
Frequently Asked Questions
Do I still need a full lighting layout if I use the wattage and lumen ranges in this guide?
Yes. The lumen and wattage ranges here are intended as starting points. For any commercial or industrial project—and even for many high‑ceiling garages—a photometric layout using .ies files provides insight into uniformity, vertical illuminance (for shelving), and glare that rules of thumb cannot capture. Layouts are also valuable evidence for meeting standards such as IES RP‑7 and energy codes.
How do I know if my existing high bays are inefficient?
Check three items on the nameplate or spec sheet: input watts, claimed lumens, and whether the product is on the DLC QPL. Divide lumens by watts to get lm/W. If the result is below roughly 125 lm/W, and the fixtures are not DLC listed, they are typically candidates for replacement with higher‑efficacy models, especially in long‑hours‑of‑use applications.
Is it okay to run high bays dimmed most of the time?
Yes. Quality LED drivers and luminaires are designed for dimming, often using 0–10 V control signals as defined in industry guidance like NEMA’s controls documents. Running fixtures at 60–80% output for much of their life can reduce thermal stress and support longer useful lifetime, provided that drivers and controls are compatible and installed according to the National Electrical Code (NEC) and manufacturer instructions.
What if my utility rebate program doesn’t require DLC listing?
Some regional programs accept custom engineering calculations or alternative qualifying lists, but using DLC‑listed, high‑efficacy high bays usually simplifies the process and provides a recognized quality screen. The DSIRE database is a good starting point to see how your local utility structures its incentives and whether DLC is referenced.
Disclaimer: This article is for informational purposes only and does not constitute professional engineering, electrical, or legal advice. Always consult a licensed design professional and qualified electrician, and review applicable local codes, standards, and utility program rules before selecting or installing lighting equipment.