How many lux per room?

Living room 150–300, kitchen 300–500, office 500 (1 fc ≈ 10.76 lux).

What utilization factor?

0.5–0.7 for medium, light-colored rooms.

How many recessed lights for a 12 × 16 ft room?

About 6–8 at 30 fc with 800 lm fixtures.

What is the maintenance factor?

Light lost over time to dirt and aging (0.7–0.8).

Lighting layout calculator

Room size, target illuminance, lumens per fixture and utilization and maintenance factors: you get how many fixtures, the grid and spacing.

Fixtures needed

12 unit

Net measurement: 9 unit

Light fixtures (full grid)12 unit
Total luminous flux needed15000 lm
Columns (along length)4 unit
Rows (across width)3 unit
Spacing along length1.5 m
Spacing across width1.33 m

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How it's calculated (visible formula)

Φ = E × area ÷ (CU × LLF); n = ceil(Φ ÷ lumens per fixture); columns ≈ √(n × length ÷ width)

Net geometric measurement, no waste.
Adjustable waste % for cuts and breakage.
Purchase rounded up to sellable units (boxes, bags, buckets, boards).

See methodology and formula versions

How to calculate it, step by step

Measure room length and width.
Pick target illuminance for the use.
Enter fixture lumens, utilization and maintenance factors.
Work out total flux and number of fixtures.
Lay them out in a grid with half spacing to the walls.

Worked example: 20 × 13 ft office at 300 lux (28 fc), 1,800 lm fixtures

Φ = 300 × 24 ÷ (0.6 × 0.8) = 15,000 lm
15,000 ÷ 1,800 = 8.3 → 9
Grid 4 × 3 = 12

→ At least 9 fixtures (12 in a 4 × 3 grid, about 5 × 4.4 ft apart).

Common mistakes

Using watts instead of lumens.
Ignoring dirt and lumen depreciation.
Not keeping half the spacing from walls.

Pro tips

Use more powerful or narrower-beam fixtures on tall ceilings.
Pick color temperature: 2700–3000 K at home, 3500–4000 K in offices.
Zone circuits or add dimming.
Check glare (UGR) at workstations.

From calculation to quote

Add labour, overhead and your margin, and generate the professional PDF.

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FAQs

How many lux per room?: Living room 150–300, kitchen 300–500, office 500 (1 fc ≈ 10.76 lux).
What utilization factor?: 0.5–0.7 for medium, light-colored rooms.
How many lumens is a 6 in LED downlight?: About 800–1,200 lm.
How many recessed lights for a 12 × 16 ft room?: About 6–8 at 30 fc with 800 lm fixtures.
What is the maintenance factor?: Light lost over time to dirt and aging (0.7–0.8).
How many foot-candles for a kitchen?: 30–50 fc on counters.

Sources and standards

Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.