Lighting

Room Lighting Calculator

Estimate total lumens and LED wattage from room area, task level, and utilization.

Lighting planning worksheet

Set the room and fixture assumptions for Room Lighting Calculator

Method for this tool

What the Room Lighting Calculator actually calculates

The engine multiplies floor area by target lux and divides by utilization, then divides the resulting lumen requirement by LED efficacy. Required source lumens include the utilization adjustment for incomplete delivery to the working plane. It is an average-area estimate, not a photometric layout; glare, shadows, uniformity, and maintenance loss are not modeled separately.

The calculation path

Area is multiplied by target lux and divided by a utilization factor; LED wattage uses selected efficacy.

Inputs that can change the answer

Room length: Enter room length in m.
Room width: Enter room width in m.
Target illuminance: Enter target illuminance in lux.
Utilization factor: Fraction of source lumens reaching the useful plane; 0.8 means 80%.
LED efficacy: Rated lumens per watt for the actual lamp or fitting.

Checks that stay outside the formula

Use separate task lights rather than over-lighting an entire room.

A practical order for entering the data

Enter the rectangular room length and width in metres.
Choose target lux for the intended activity and a utilization factor supported by the proposed lighting arrangement.
Enter the actual LED efficacy in lumens per watt and compare the output with fixture specifications.

Project walkthrough: Lighting: from lumen estimate to fixture layout

Project walkthrough: Plan a bedroom from bed size to wardrobes and walkways

Project walkthrough: Build a layered kitchen lighting plan around tasks

Project walkthrough: Plan bathroom lighting without treating a lumen figure as approval

Engine check using the prefilled sample

Lighting example: room length = 5 m, room width = 4 m, target illuminance = 200 lux, utilization factor = 0.8 and led efficacy = 90 lm/W. Treat these as demonstration room and fixture values, then recalculate with the dimensions and rated output of the fittings you are considering.

Results for these inputs

Room area: 20.00 m²
Required source lumens: 5,000 lm
Approximate LED wattage: 55.56 W

Project-specific method

Worked example and purchase checks

The tool uses floor area and target illuminance to estimate lumens at the working plane, adjusts by the entered utilization factor, and converts the result to an approximate LED wattage using the entered efficacy.

Illustrative worked example

A 4.8 m × 3.9 m living room using a moderate target and an explicit utilization assumption for early fixture comparison.

Exact inputs for this example

Room length	4.8 m
Room width	3.9 m
Target illuminance	180 lux
Utilization factor	0.72
LED efficacy	95 lm/W

Room area: 18.72 m²
Required source lumens: 4,680 lm
Approximate LED wattage: 49.26 W

How to read the result

Use the lumen figure to compare fixture combinations, then verify the exact fixture output and distribution. For kitchens, desks, mirrors, or artwork, plan the task/accent layer separately.

Assumptions this example makes

Target lux, utilization factor, and LED efficacy are planning inputs supplied by the visitor.
The room is treated as one lighting zone.

What this calculator does not prove

It does not perform a photometric calculation, account for beam angles, surface reflectance, maintenance factors, glare, or task-specific placement.
Wattage is derived from efficacy and should not be used to choose fixtures when lumen data are available.

Room-level lighting estimateSketch is explanatory, not to scale.

Mistakes that change this result

Using fixture wattage as if every LED has the same efficacy.
Treating a room-level lumen total as a fixture-spacing plan.
Ignoring task lighting and dark finishes that affect useful light.