Lighting Design Tool
Light Fixture Count Calculator
How many LED track lights or downlights do you need per room? Enter your room size, target illuminance and fixture wattage to get the exact fixture count and a suggested grid layout.
Lux / Fixture Count Calculator
Room & target
Target: 300–750 lux (retail general)
Result
Floor area
48 m²
Required light output
52,500 lm
Formula: total lumens = target lux × floor area × loss factor
Recommended fixtures
32 fixtures
Suggested layout
5 rows × 7 cols (35 positions)
How the lux calculator works
- Work out the floor area: length × width.
- Pick the target illuminance for your application (retail 300–750 lux, office 300–500 lux, warehouse 150–300 lux).
- Multiply: total lumens = target lux × floor area × loss factor (loss factors cover dirt, lamp depreciation and room utilization).
- Divide by the lumen output of your chosen fixture (fixture lumens = wattage × lm/W) and round up to get the number of fixtures.
Tip: use the beam angle calculator first to size the beam spread at your mounting height, then this lux calculator to size the quantity.
Spacing & Layout Rules of Thumb
1. Spacing vs. mounting height
For flood beams (36°+), space fixtures at 1.0–1.5× the mounting height. For spot beams (10°–24°), reduce spacing to 0.5–1.0× to avoid dark pools between fixtures.
2. Aim for uniformity
The beam diameter at the work plane should overlap its neighbour by about 20–30% for even illumination. Use the beam angle calculator to check the spot size at your mounting height.
3. Perimeter rule
Keep the outer row of fixtures about half a spacing distance from the walls — this lights the walls without creating harsh shadows, and improves the perceived brightness of the room.
FAQs
Fixture Quantity Questions
Common questions about how many lights a room needs.
How do I calculate how many light fixtures I need?
Required lumens = target lux × floor area × loss factor. Then divide by the lumen output of one fixture (wattage × efficacy) and round up. The calculator above does it for you.
What spacing should I use between LED track lights?
Start with 1.0–1.5× the mounting height for flood beams and closer for spots. Our calculator suggests a grid from your room size and fixture count.
How many downlights do I need for a living room?
A typical 20 m² living room at 150–300 lux needs roughly 4–6 × 10W LED downlights. Precise numbers depend on target lux, fixture lumen output and loss factors.
Should I use more, lower-wattage fixtures or fewer, higher-wattage ones?
More lower-wattage fixtures with a wider beam give more uniform light and lower glare; fewer high-wattage spots create dramatic pools of light. For retail and general commercial, uniformity usually wins.
Let Our Engineers Design the Layout
Send us your room plan and target lux — we will return a free photometric layout with fixture recommendations.