Lighting Layout Calculator
Calculate the number and spacing of light fixtures needed for target lux levels. Enter values for instant results with step-by-step formulas.
Formula
N = (E x A) / (F x UF x MF)
Where N = number of fixtures, E = target illuminance in lux, A = room area in square meters, F = lumens per fixture, UF = utilization factor (fraction of light reaching work plane), and MF = maintenance factor (depreciation allowance). The room index K = (L x W) / (Hm x (L + W)) determines the utilization factor.
Worked Examples
Example 1: Office Lighting Layout
Problem: Design the lighting layout for a 12m x 10m office needing 500 lux. Using 3,600-lumen LED panels at 36W each, mounted at 2.8m with 0.75m work plane. MF = 0.80, UF = 0.50.
Solution: Area = 12 x 10 = 120 sqm\nTotal lumens needed = (500 x 120) / (0.50 x 0.80) = 150,000 lumens\nNumber of fixtures = 150,000 / 3,600 = 41.7 = 42 fixtures\nGrid: sqrt(42 x 12/10) = 7.1 -> 8 along length\nFixtures along width = 42/8 = 5.25 -> 6\nActual fixtures = 8 x 6 = 48\nSpacing: 12/8 = 1.5m x 10/6 = 1.67m
Result: 48 fixtures in 8x6 grid | Spacing: 1.5m x 1.67m | Actual lux: 576 | Total: 1,728W (14.4 W/sqm)
Example 2: Warehouse Lighting
Problem: Design lighting for a 30m x 20m warehouse needing 200 lux. Using 18,000-lumen high-bay LED fixtures at 150W, mounted at 8m height, 0.0m work plane. MF = 0.70, UF = 0.45.
Solution: Area = 30 x 20 = 600 sqm\nTotal lumens = (200 x 600) / (0.45 x 0.70) = 380,952 lumens\nFixtures = 380,952 / 18,000 = 21.2 = 22 fixtures\nGrid: sqrt(22 x 30/20) = 5.7 -> 6 along length\nAlong width = 22/6 = 3.67 -> 4\nActual = 6 x 4 = 24\nSpacing: 30/6 = 5.0m x 20/4 = 5.0m\nSHR = 5.0 / 8.0 = 0.625
Result: 24 fixtures in 6x4 grid | Spacing: 5.0m x 5.0m | SHR: 0.63 | Total: 3,600W (6.0 W/sqm)
Frequently Asked Questions
What is the lumen method for lighting design?
The lumen method, also called the zonal cavity method, is the most widely used technique for calculating the number of luminaires needed to achieve a desired illuminance level in a room. It works by calculating the total lumens required using the formula: Number of Fixtures = (Target Lux x Area) / (Lumens per Fixture x Utilization Factor x Maintenance Factor). The method assumes a uniform distribution of light across the work plane and accounts for room proportions through the room index, light losses due to aging and dirt through the maintenance factor, and the fraction of light that reaches the work plane through the utilization factor. It is the standard method taught in lighting design courses worldwide.
What is the room index and how does it affect lighting?
The room index (also called room cavity ratio or K factor) is a dimensionless number that describes the proportions of a room relative to the mounting height of the luminaires above the work plane. It is calculated as K = (Length x Width) / (Mounting Height x (Length + Width)). A room index below 1.0 indicates a tall, narrow room where much light is absorbed by walls before reaching the work plane. A room index above 3.0 indicates a wide, low room where most light reaches the work plane efficiently. The room index determines the utilization factor from manufacturer tables, with higher room indices giving better light utilization. Most practical rooms have a room index between 0.75 and 5.0.
What is the maintenance factor in lighting calculations?
The maintenance factor (MF) accounts for the reduction in light output over time due to lamp lumen depreciation, luminaire dirt accumulation, and room surface degradation. A new installation produces more light than it will after several years of use. Typical maintenance factors range from 0.60 for dirty industrial environments with infrequent cleaning to 0.80 for clean offices with regular maintenance. LED luminaires have higher maintenance factors (0.85 to 0.90) because they depreciate more slowly and accumulate less heat to attract dust. Using a maintenance factor that is too high leads to insufficient light after a few years, while too low wastes energy from the start.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
How accurate are the results from Lighting Layout Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.
Is Lighting Layout Calculator free to use?
Yes, completely free with no sign-up required. All calculators on NovaCalculator are free to use without registration, subscription, or payment.