Lighting Layout Calculator
Fixture counts the way lighting design actually works — the lumen method with its assumptions in the open. Pick a space type for an IES-range footcandle target, pick a real fixture (troffer, high bay, strip, downlight), and get the count, a spacing-criterion-checked grid, delivered footcandles after coefficient of utilization and light loss, the ASHRAE 90.1 watts-per-square-foot check, and a dimensioned room map you can print onto a quote. Free, no login.
Room & fixture
Assumptions (CU, light loss, spacing criterion)
Layout sheet header (project, room, preparer)
Layout
Lumen method: N = (fc × area) ÷ (lumens × CU × LLF), delivered LM-79 lumens, maintained fc at the floor. Targets: IES-generation design ranges. LPD: ASHRAE 90.1-2019 Table 9.6.1. Average illuminance only — a stamped photometric layout (AGi32/DIALux) governs where specified.
Lighting Layout Sheet
Lumen-method fixture layout — prepared with the NORDIX Lighting Layout Calculator (nordixhq.com/tools/lighting-layout-calculator)
| Project: — | Room / area: — |
| Prepared by: — | Date: — |
| Space | Warehouse — open / aisles — 200 × 100 ft (20,000 ft²), ceiling 26 ft, mounting 23 ft |
| Target | 20 fc maintained (10–30 fc IES-range, floor) |
| Fixture | 32 × UFO high bay — 150 W — 21000 lm delivered, 150 W each |
| Layout | 4 rows × 8 columns; spacing 25 × 25 ft; first fixture 12.5 / 12.5 ft from the walls |
| Delivered illuminance | 20.2 fc maintained average (CU 0.75, LLF 0.8, RCR 1.7) |
| Uniformity check | Spacing within SC 1.2 × 23 ft mounting height — acceptably uniform per the fixture spacing criterion |
| Lighting power density | 0.24 W/ft² vs 0.33 W/ft² allowance (ASHRAE 90.1-2019 Table 9.6.1) — COMPLIES |
Method: lumen (zonal-cavity) method — average maintained illuminance only; point-by-point uniformity is not computed. Delivered lumens per LM-79; no ballast factor applies to LED. Footcandle targets are IES-generation design values as published in free reproductions (Lighting Design Lab / Elite Lighting / Archtoolbox). LPD allowances per ASHRAE 90.1-2019 Table 9.6.1 (IECC 2021 is nearly identical; adopted editions vary — verify locally). This is a planning estimate for quoting and sanity checks, not a stamped photometric layout.
How this calculator works
The lumen method computes the fixtures needed to hold an average maintained illuminance:
N = (target fc × area) ÷ (delivered lumens × CU × LLF)
Every term matters, and the quickie calculators skip two of them. Delivered lumens are the fixture’s LM-79 figure (LED needs no ballast factor — the driver is already in the number). The coefficient of utilization is the fraction of those lumens that actually reach the work plane — it falls as rooms get taller and smaller, which this tool estimates from the room cavity ratio (RCR = 5 × cavity height × (L + W) ÷ (L × W)) and lets you override from the fixture’s photometric report. The light loss factor (default 0.80) covers LED aging and dirt. Skipping CU and LLF overstates brightness by 30–50%, which is why calculators disagree — this one shows its assumptions. The grid then has to pass the fixture’s spacing criterion — maximum spacing = SC × mounting height above the work plane, the industry definition of “acceptably uniform” — so the layout is honest about dark stripes, not just total lumens. Wall offsets are half the fixture spacing, the universal convention.
Worked example: a 100×200 ft warehouse
- Target 20 fc (open warehouse), 150 W UFO high bays at 21,000 delivered lumens, mounted at 23 ft, CU 0.75, LLF 0.8.
- N = (20 × 20,000) ÷ (21,000 × 0.75 × 0.8) = 31.7 → 32 fixtures.
- Grid: 4 rows × 8 columns at 25 × 25 ft, first row 12.5 ft off the walls — S/MH = 25/23 = 1.09, inside the 1.2 spacing criterion.
- Delivered: 20.2 fc. Power: 32 × 150 W ÷ 20,000 ft² = 0.24 W/ft² — well under the 0.33 W/ft² warehouse allowance (ASHRAE 90.1-2019).
These are the default inputs above — the map, dimensions, and compliance lines are exactly what the high-bay vendors make you email them and wait days for.
Reference: footcandle targets and power allowances
Maintained horizontal footcandles at the 30 in work plane (corridors, warehouses, and circulation at the floor) — IES-generation design ranges as published in free reproductions (Lighting Design Lab, Elite Lighting, Archtoolbox). LPD allowances per ASHRAE 90.1-2019 Table 9.6.1 (IECC 2021 is nearly identical; the 2022 edition tightens offices and retail).
| Space | Design target | Range | LPD allowance |
|---|---|---|---|
| Office — open plan | 40 fc | 30–50 fc | 0.61 W/ft² |
| Office — private/enclosed | 40 fc | 30–50 fc | 0.74 W/ft² |
| Conference room | 30 fc | 30–50 fc | 0.97 W/ft² |
| Classroom | 40 fc | 30–50 fc | 0.71 W/ft² |
| Corridor | 10 fc | 5–20 fc | 0.44 W/ft² |
| Stairwell | 10 fc | 5–10 fc | 0.49 W/ft² |
| Warehouse — bulky items | 10 fc | 10–20 fc | 0.33 W/ft² |
| Warehouse — open / aisles | 20 fc | 10–30 fc | 0.33 W/ft² |
| Warehouse — small-item picking | 30 fc | 15–60 fc | 0.69 W/ft² |
| Retail sales area | 50 fc | 20–80 fc | 1.05 W/ft² |
| Commercial kitchen / food prep | 50 fc | 30–100 fc | 1.09 W/ft² |
| Mechanical / electrical room | 30 fc | 20–50 fc | 0.43 W/ft² |
| Restroom | 18 fc | 7.5–30 fc | 0.74 W/ft² |
| Gym / exercise area | 30 fc | 20–50 fc | 0.9 W/ft² |
| Loading dock (interior) | 20 fc | 10–30 fc | 0.88 W/ft² |
| Parking garage (covered) | 5 fc | 5–10 fc | 0.15 W/ft² |
| Workshop / garage shop | 30 fc | 30–75 fc | 1.26 W/ft² |
| Residential kitchen (ambient) | 25 fc | 10–30 fc | — |
| Residential living / bedroom | 15 fc | 5–20 fc | — |
Reference: fixture presets
Representative delivered-lumen and wattage values from current datasheets and listings — every value editable, and your fixture’s cut sheet governs. Spacing criteria are typical for the type; the photometric file has the real number.
| Fixture | Delivered lm | Watts | lm/W | Typical SC |
|---|---|---|---|---|
| 2×4 LED troffer | 5,000 | 45 | 111 | 1.3 |
| 2×2 LED troffer | 3,500 | 30 | 117 | 1.3 |
| 6-in LED downlight / wafer | 1,000 | 12 | 83 | 1 |
| 4-ft LED strip | 5,000 | 35 | 143 | 1.3 |
| 8-ft LED strip | 10,000 | 64 | 156 | 1.3 |
| 4-ft wraparound | 4,800 | 38 | 126 | 1.3 |
| 4-ft vapor-tight | 4,500 | 38 | 118 | 1.3 |
| UFO high bay — 100 W | 14,000 | 100 | 140 | 1.2 |
| UFO high bay — 150 W | 21,000 | 150 | 140 | 1.2 |
| UFO high bay — 200 W | 28,000 | 200 | 140 | 1.2 |
Frequently asked questions
How many light fixtures do I need for my room?
Use the lumen method: fixtures = (target footcandles × area) ÷ (delivered lumens per fixture × coefficient of utilization × light loss factor). A 30×40 ft office at 35 fc with 5,000-lumen troffers, CU 0.65 and LLF 0.8 works out to 42,000 ÷ 2,600 = 16.2 → 17 fixtures minimum, snapped to a practical grid. The two factors most free calculators skip — CU and LLF — are the difference between a real answer and one that's 30–50% too optimistic. This calculator shows both, defaults them sensibly, and lets you override from the fixture's photometric report.
How many footcandles do I need?
By space: offices and classrooms 30–50 fc (40 typical) at the 30-inch work plane; conference rooms 30; corridors and stairs 5–10 at the floor; open warehouses 10–30 (20 typical), fine-picking areas up to 60; retail sales floors 20–80 (50 typical); commercial kitchens 50+; covered parking 5; residential living spaces 10–20 and kitchen ambient 20–30 with 30–50 on the counters. These are IES-generation maintained-illuminance design ranges — 'maintained' meaning after the fixture ages and gets dirty, which is what the light loss factor accounts for.
What is a coefficient of utilization and why does it matter?
CU is the fraction of a fixture's lumens that actually reach the work plane — the rest is absorbed by walls and ceiling. It comes from the fixture's zonal-cavity table indexed by the room cavity ratio, RCR = 5 × cavity height × (L+W) ÷ (L×W): a big open warehouse might run 0.75, a typical office 0.6–0.7, a tall narrow room 0.5 or less. This calculator estimates CU from your room's RCR (assuming light 80/50/20 reflectances) and lets you enter the real value from the fixture's photometric report. Ignoring CU is why the 'lumens per square foot' quickie calculators under-light real rooms.
How far apart should light fixtures be?
Within the fixture's spacing criterion: maximum spacing = SC × mounting height above the work plane — the industry definition of 'acceptably uniform.' Typical SC values run about 1.2–1.4 for troffers and strips, 1.0–1.5 for high bays, and around 1.0 for downlights, with the real number in each fixture's photometric file. Set fixtures half the spacing off the walls. The residential rule of thumb — recessed cans spaced at half the ceiling height, a quarter from walls — is a crude version of the same idea; this calculator checks the actual criterion and warns when a lumen-minimum grid would leave dark stripes.
How many high bay lights does my warehouse need?
Worked example: a 100×200 ft warehouse at 20 fc with 150 W UFO high bays (21,000 delivered lumens) mounted at 23 ft needs (20 × 20,000) ÷ (21,000 × 0.75 × 0.8) = 32 fixtures — a 4×8 grid at 25-foot spacing, 12.5 ft off the walls, with S/MH = 1.09 inside the 1.2 spacing criterion and 0.24 W/ft² against a 0.33 allowance. Current UFO high bays run about 140 lm/W: 100 W ≈ 14,000 lm, 150 W ≈ 21,000, 200 W ≈ 28,000. This calculator draws that layout instantly — no emailing a vendor and waiting days for a free layout that's really a sales quote.
What is lighting power density and what's the limit?
LPD is total fixture watts divided by floor area, and energy codes cap it by space type: ASHRAE 90.1-2019 allows 0.61 W/ft² in open offices, 0.71 in classrooms, 0.44 in corridors, 0.33 in bulk warehouses, 1.05 in retail, and 1.09 in commercial kitchens (IECC 2021 is nearly identical; 90.1-2022 tightens offices and retail further). Modern LED layouts usually comply easily — the warehouse example lands at 0.24 W/ft² — but over-lighting with high-wattage fixtures can still bust the allowance. This calculator prints your computed W/ft² against the allowance on every layout, a check no other free tool performs.
Lumens or watts — which should I use to pick fixtures?
Lumens — watts measure consumption, not light. LED efficacy varies enough that wattage alone is meaningless: lensed troffers deliver about 110–125 lm/W, linear strips and high bays 140–160, deep-baffle downlights 90–100. Use the delivered (LM-79) lumen figure from the datasheet, not 'wattage equivalent' marketing numbers, and note that for LED there is no ballast factor — driver losses are already inside the delivered-lumens figure. This calculator's presets carry real datasheet pairs, and every value is editable.
Is this a substitute for a photometric layout?
No — it's the planning layer. The lumen method gives the average maintained illuminance and this tool adds the spacing-criterion uniformity check, which is enough to count fixtures for a bid, sanity-check a vendor's proposal, or lay out a garage. It does not compute point-by-point illuminance, max/min uniformity ratios, glare, or vertical footcandles — when a spec calls for a stamped photometric plan, that's AGi32 or DIALux territory with the fixture's actual .ies files. The printable sheet states its assumptions (CU, LLF, targets) so a reviewer can see exactly what was claimed.
Method: lumen (zonal-cavity) method — average maintained illuminance; point-by-point uniformity is not computed, and the only uniformity claim made is the spacing-criterion check (max spacing = SC × mounting height above the work plane). Footcandle targets are IES-generation design values via free published reproductions; ranges shown, targets editable. LPD allowances per ASHRAE 90.1-2019 space-by-space (Table 9.6.1); adopted editions vary by state and 90.1-2022 tightens several categories — verify locally, and note the space-by-space method’s extra room-geometry allowances are not modeled. This is a planning estimate for quoting and design sanity checks — where a stamped photometric plan is specified, AGi32/DIALux and the fixture’s .ies files govern.
Wire the layout with the Voltage Drop Calculator and Wire Ampacity Calculator, or estimate the circuit count with the Service & Load Calculator.