How many lumens do I need per square meter?

It depends on the room type. A bedroom needs about 150–200 lux, a kitchen 400–500 lux, an office 300–500 lux. Multiply the required lux by the room area to get total lumens needed, then divide by the lumens per fixture.

How many lumens does an LED bulb produce?

A typical LED equivalent to a 60 W incandescent produces around 800 lumens. A 100 W equivalent produces about 1,600 lumens. LEDs produce approximately 80–120 lumens per watt, compared to 10–15 lumens per watt for incandescents.

What lux level do I need for a home office?

IES recommends 300–500 lux for office tasks involving reading and writing. For a home office, aim for 400–500 lux at the work surface. Task lighting (a desk lamp) can supplement ambient ceiling fixtures to achieve the required level.

Lighting Calculator

Q: What is the difference between lumens and lux?

Lumens measure the total light output of a bulb or fixture. Lux measures the illuminance — how much light falls on a surface per square meter. 1 lux = 1 lumen per m². The lux you achieve depends on lumens, room area, and the coefficient of utilization.

Calculate how many light fixtures you need for any room — bedrooms, kitchens, offices and more — based on IES illuminance targets and fixture lumens.

What this calculates

Calculates the number of fixtures needed to reach the recommended illuminance for the selected room type, the actual lux achieved, and the estimated total installed power assuming LED sources.

Formula used

Fixtures = ceil((target lux × area) ÷ (lumens × CU × FM)). CU (coefficient of utilization) = 0.65. FM (maintenance factor) = 0.80. Watts estimated at 1 W per 100 lm (LED).

Worked example

A 4 m × 3 m bedroom (12 m²) at 150 lux with 800 lm fixtures: fixtures = ceil((150 × 12) ÷ (800 × 0.65 × 0.80)) = ceil(1800 ÷ 416) = ceil(4.3) = 5 fixtures. Total: 5 × 8 W = 40 W.

IES illuminance targets

Hallway / storage: 100 lux. Bedroom: 150 lux. Living room: 200 lux. Bathroom: 300 lux. Office / kitchen / workshop: 500 lux. These are ambient (general) lighting targets; task areas benefit from additional local lighting.

When not to use this calculator

This calculator handles simple rectangular rooms with uniform ceiling fixtures. Complex layouts, architectural lighting, emergency lighting, retail or industrial spaces require a photometric design using dedicated lighting software.

How to use this calculator

Enter the room length and width in meters.
Select the room type — this sets the IES-recommended target illuminance automatically (100–500 lux depending on use).
Enter the lumens per fixture — check the LED package. Common values: recessed downlight 400–800 lm; surface pendant 800–1,500 lm; track spotlight 300–600 lm per head.
Click "Calculate lighting" to see fixture count, actual lux achieved and total installed wattage.

Illuminance standards — IES, EN 12464-1 and AS/NZS 1680

The illuminance targets used in this calculator are based on international standards for ambient general lighting. Task areas typically require additional local lighting:

Hallway / corridor (100 lux): IES RP-28, EN 12464-1. Adequate for safe movement. Occupancy sensors recommended.
Bedroom (150 lux): General ambient target. Add bedside reading lamps for 300 lux at the pillow level.
Living room (200 lux): General viewing. Add accent lighting for video display areas (reduce ambient to 50 lux).
Bathroom / bathroom vanity (300 lux): General. Add mirror task lighting (500 lux horizontal at face level) for shaving and makeup.
Kitchen / office / workshop (500 lux): IES / EN 12464-1 for task-oriented spaces. Supplement with under-cabinet task lighting in kitchens.

CU and FM — what the calculation factors mean

This calculator uses two multipliers that account for real-world losses:

CU = 0.65 (Coefficient of Utilization): Not all light from a fixture reaches the work plane — some is absorbed by walls, ceiling and furnishings. 0.65 assumes light-colored walls (reflectance ~70%) and a typical room geometry. Dark-colored rooms may use CU = 0.45–0.55, requiring more fixtures.
FM = 0.80 (Maintenance Factor / Light Loss Factor): Lamps depreciate over time and fixtures collect dust. FM = 0.80 means the system will produce 80% of its initial output over its rated life — a realistic baseline for LED fixtures in normal environments.

Frequently asked questions

How many lumens do I need per m²?

Multiply the required lux by the room area to get total lumens needed (before CU/FM losses). A 150-lux bedroom of 12 m² needs a theoretical 1,800 lm, but about 2,900 lm accounting for losses.

What is the difference between lumens and lux?

Lumens = total light output of a source. Lux = lumens per m² at the work plane. 1 lux = 1 lm/m².

How many lumens does an LED produce?

Typical LEDs: 80–120 lm/W. A 10 W LED produces roughly 800–1,000 lm. This calculator estimates 100 lm/W for budget purposes.

What lux do I need for a home office?

400–500 lux for general ambient lighting. Supplement with a dedicated desk lamp for the work surface to reach 300–500 lux at the task plane.

Assumptions

Coefficient of utilization (CU): 0.65 (average room with light-colored walls).
Maintenance factor (FM): 0.80 (accounts for dust and lumen depreciation over time).
LED efficacy estimate: 100 lm/W (1 W per 100 lm).
Uniform ambient lighting in a rectangular room — no task or accent lighting modeled.

Technical note

Actual illuminance depends on fixture type, ceiling height, room reflectances and lamp position. For critical applications use photometric software (DIALux, Relux, AGi32) with manufacturer IES files.

Common mistakes

Using watts instead of lumens — newer LED equivalents make wattage misleading.
Forgetting that ceiling height reduces effective lux at the work plane.
Not adding task lighting in kitchens and offices where 500 lux is needed locally.

Related calculators

BTU / Heating

Heating and cooling load in kW and BTU/h for the same room.

Open

Solar Panels

Panel count and kWp to supply the room's electrical load from solar.

Open

Drop Ceiling

Suspended ceiling grid and tiles where the fixtures will be recessed.

Open