Wattage per square meter (W/m²) for factory lighting is the installed electrical load of luminaires divided by the floor area. It's your primary tool for estimating energy demand and checking compliance with energy codes like EN 15193 or ASHRAE 90.1. But don't confuse it with illuminance — it's a power budget, not a brightness target.
Recommended Values by Application
Application Scenario
Recommended W/m²
Standard
High-bay warehouse (storage only, 8–12m height)
3–5 W/m²
EN 12464-1:2021, Table 5.1
General assembly (precision work, 500 lx target)
8–12 W/m²
EN 12464-1:2021, Table 5.2
Electronics manufacturing (1000 lx, cleanroom)
12–18 W/m²
IESNA RP-7-21, Section 4.3
Warehouse with mezzanine (mixed storage + picking)
5–8 W/m²
EN 15193-1:2021, Annex C
Heavy machinery / welding bay
10–15 W/m²
CIE S 008/E:2001, Table 3
Paint shop / finishing (color rendering critical)
9–13 W/m²
EN 12464-1:2021, Table 5.4
Cold storage / freezer (-20°C)
4–7 W/m²
IEC 60598-2-24:2013, Clause 5.2
Office area within factory (300–500 lx)
6–9 W/m²
EN 12464-1:2021, Table 5.5
Specification Comparison
Parameter
Minimum
Standard
Premium
Luminaire efficacy (lm/W)
90 lm/W
120–140 lm/W
160–180 lm/W
W/m² achieved (at 500 lx, 8m height)
14 W/m²
9 W/m²
6 W/m²
Control system
Manual on/off
Daylight harvesting + occupancy
BMS-integrated, adaptive zoning
Lifetime (L70 at 25°C)
30,000 h
50,000 h
100,000 h
Power factor
>0.85
>0.90
>0.95
Why Wattage Per Square Meter Factory Matters
Let's put numbers to this. A 10,000 m² factory running at 12 W/m² pulls 120 kW of lighting load. At €0.12/kWh and 4,000 hours per year, that's €57,600 annually — just for lights. Drop that to 8 W/m² with better fixtures and controls, and you're at €38,400. That's a €19,200 saving every year.
Here's the thing: most energy codes now cap lighting power density. EN 15193-1:2021 sets a maximum of 10 W/m² for general industrial spaces, but local variants can be stricter. I've seen projects where the client specified 7 W/m² and we had to use 160 lm/W LED high-bays with occupancy sensors to hit it. The catch is that lower W/m² often means more fixtures — you trade power for uniformity.
What does this mean in practice? If you're designing a new line, you need to calculate the target illuminance from EN 12464-1 first, then work backward to find the minimum W/m² that meets it. Don't just pick a number from a table — that's how you end up with dark corners or blinding hot spots. I've been on site where a "standard" 10 W/m² design left a 50 lx shadow under a mezzanine because nobody checked the actual layout.
Application Scenarios
**Scenario 1: High-bay warehouse, 12m clear height, 5,000 m².** Target illuminance is 150 lx per EN 12464-1 for storage. Using 140 lm/W high-bays with narrow optics, you'll need about 4.5 W/m². That's 22.5 kW total. Add occupancy sensors (30% reduction factor per EN 15193) and you're at 15.75 kW average. Fixture recommendation: 150W LED high-bay, 21,000 lm, IP65, 5000K.
**Scenario 2: Precision assembly line, 8m height, 2,000 m².** Target is 750 lx with Ra ≥ 80. You'll need 10–12 W/m² with standard panels, but premium 160 lm/W troffers can get you to 8 W/m². Use 2'x4' LED panels at 50W each, 8,000 lm, with dimming down to 10%. I'd spec a DALI system here — the line workers will thank you when they can adjust task lighting without calling maintenance.
**Scenario 3: Cold storage at -20°C, 1,000 m².** Target is 200 lx, but the real challenge is the electronics. Use LED fixtures rated for -30°C per IEC 60598-2-24. Expect 5–7 W/m² because the drivers lose efficiency in the cold. Don't use standard drivers — they'll fail in six months. I learned that one the hard way.
**Scenario 4: Paint booth, 500 m², Ra ≥ 90 required.** Target is 500 lx with CRI > 90. You'll need 12–15 W/m² because high-CRI LEDs are less efficient — typically 100–110 lm/W. Use sealed IP65 fixtures with tempered glass. And for god's sake, make sure they're rated for explosive atmospheres if you're spraying solvent-based paints (ATEX Zone 1).
Design Guidelines
Start with the target illuminance from EN 12464-1:2021, Table 5.1–5.5. For general factory work, that's 300–500 lx. Then calculate the required lumens: lux × area × maintenance factor (typically 0.8 for clean, 0.7 for dirty). Divide by luminaire efficacy to get watts. That's your W/m².
Here's a rule of thumb I use: for a 500 lx target at 8m height with 130 lm/W fixtures, expect 8–10 W/m². Every 1m increase in mounting height adds about 1 W/m² due to light loss. Every 50 lm/W improvement in efficacy cuts W/m² by about 30%.
Controls are where the real savings live. EN 15193-1:2021 allows a 30–50% reduction in calculated W/m² if you use daylight harvesting and occupancy sensing. I've seen projects hit 5 W/m² with full controls and premium fixtures. But don't forget the commissioning — a poorly tuned sensor is worse than none.
Bottom line: always run a lighting calculation in software like Dialux or Relux. The W/m² tables are starting points, not guarantees. I've had to re-spin entire designs because the client's "standard" W/m² didn't account for rack shadows or column spacing.
Key Takeaways
Key Takeaway: Wattage per square meter for factories is a power budget, not a brightness spec. Use EN 12464-1 to set illuminance targets, then calculate W/m² from fixture efficacy and layout. Target 6–10 W/m² for most industrial spaces with modern LED gear, but expect 12–18 W/m² for high-CRI or cleanroom applications. Controls can cut your energy use by 30–50% — spec them from day one. Always verify with a photometric calculation before ordering fixtures.