Interactive lighting calculator

Lighting Layout and Spotlight Quantity Calculator

Enter room dimensions, mounting height, and fixture lumens to calculate fixture quantity, maintained lux, spacing, and the distance from each wall on a responsive reflected ceiling plan.Start calculating

lux / lmLux and lumensPDFStandalone reportIES Lumen MethodMethod reference

Calculator

Enter your data and see the result immediately

Create an interactive lighting plan and calculate spotlight quantity, lux, lumens, spacing, and wall offsets using a complete grid or open-corner perimeter with an optional centre fixture.

Calculator

Lighting design and layout

Visual layout with spacing and lux

Calculation inputsResults update instantly

Calculation mode

Lumen source

Spacing criterion SC source

Space typeTarget illuminance

lux

Layout patternLength

Width

Mounting height

Workplane height

Fixture lumens from datasheet

Fixture wattage

Beam angle

Utilization factor CU

Maintenance factor MF

With product lumens entered, watts affect energy only; brightness follows actual lumens.

Study resultTAYAR TK

Preliminary engineering studyLighting design and layout

Date: 2026-07-23Report reference: KWH-LIGHTING-2026

Lighting fixture layout

Uniform engineering grid for 30 m², recalculated directly from lumens, area, and design factors.

Lighting fixture quantity20fixtures

Maintained average illuminance288lux

Effective lumens per fixture900lm

Installed power180W

Actual room size 6 × 5 mSpacing 1.2 × 1.25 mFirst-centre wall offset 0.6 × 0.63 mHeight above workplane 2.2 mSpacing criterion SC 0.65*Sx/MH × Sy/MH 0.55 × 0.57Nominal beam diameter 1.43 mInside nominal beam footprints 90.07%Spacing check Preliminarily good

Layout patternUniform engineering grid

Calculated minimum before layout rounding20 fixtures

Minimum from average illuminance14 fixtures

Minimum from spacing criterion SC20 fixtures

Nominal spacing1.2 × 1.25 m

First-centre wall offset0.6 × 0.63 m

Applied spacing criterion SC0.65 (estimated from beam angle)

Theoretical beam diameter1.43 m

Spacing ratio Sx/MH × Sy/MH0.55 × 0.57

Central fixture decisionNot included; the layout is calculated without a chandelier

Layout symmetry about both axesVerified

Preliminary coverage checkPreliminarily consistent with SC and coverage

Area inside nominal beam footprints90.07%

Farthest point from a fixture0.87 m

Nominal / maintained lumens18,000 / 8,640 lm

Room index1.24

Lighting power density6 W/m²

Calculation method

Final quantity is the greater of the lumen method and the SC × mounting-height spacing limit. The grid is completed symmetrically; perimeter fixtures are balanced on opposite sides with frame-corner intersections excluded.

Engineering notes

Datasheet lumens are used; wattage alone changes energy use, not light output, because lumens are the photometric quantity.
The grid uses approximately half a cell at the wall and keeps complete symmetric rows and columns; no fixture sits on a wall or at the physical room corner.
A chandelier is not an automatic calculation requirement; add a central fixture only when the architectural concept needs it, then identify whether it is decorative or functional.
The current SC is a conservative estimate derived from beam angle. Replace it with the IES or product-datasheet SC when available.
This is a lumen-method calculation and preliminary engineering layout; point-by-point results require an IES/LDT file, surface reflectance, and a calculation grid in DIALux or equivalent software.

Safety approval

Uniformity U0, glare UGR, and minimum/maximum values cannot be derived from lumens and beam angle alone; actual photometry is required.

This is a planning and comparison estimate. Final protection and conductor selection requires review by a licensed engineer or electrician, site-condition checks, manufacturer instructions, and the applicable code.

Calculation guide

How does the lighting layout calculator work?

The study starts with room area, target illuminance, and actual lumens per fixture. It applies the lumen method for maintained average illuminance, then checks spacing criterion SC against mounting height. Enter the product or IES value when available; otherwise the calculator clearly labels its beam-angle estimate as preliminary.

Choose a uniform grid, a grid with a centre fixture, an open-corner perimeter, or a perimeter with a centre fixture. Opposite perimeter sides receive equal quantities, frame intersections remain free of spotlights, and the plan separates perimeter-row setback from corner clearance to the first fixture centre.

A chandelier is never forced. A decorative centre appears on the plan but is excluded from illuminance and fixture reduction; it contributes only when marked as functional and supplied with documented lumens and beam data.

This is a preliminary design result. Uniformity, glare, minimum and maximum illuminance require real IES or LDT photometry, surface reflectance, and a point-by-point DIALux calculation.

How to calculate room spotlight quantity

Choose the space type to load an editable starting illuminance.
Enter length, width, ceiling height, and workplane height.
Use datasheet lumens or estimate lumens from watts and efficacy.
Choose the layout and beam angle, then review spacing and wall offsets.
Export the active lighting layout and study as a standalone PDF.

What should be checked before installation?

Actual lumens, not wattage alone, determine light output.
A luminaire's published SC is more reliable than inferring spacing from beam angle alone.
Grid wall offset means wall-to-first-centre; perimeter setback and corner clearance are separate dimensions.
A perimeter may meet average lux yet leave the room centre under-covered, so coverage is reported separately.
A chandelier requires documented lumen and distribution data before counting as general light.
Task zones may need local lighting even when average lux is adequate.

Method references

IES Lumen Method IES Spacing Criterion EN 12464-1 DIALux

Frequently asked questions

Interactive lighting calculator frequently asked questions

What is the correct distance between spotlights?

It follows room dimensions and the completed grid and is checked against SC × mounting height. No single spacing works for every luminaire and project.

How far should a spotlight be from the wall?

A uniform grid starts at half a layout cell. A perimeter has two separate dimensions: wall-to-row setback and corner-to-first-centre clearance.

Should a spotlight sit at a perimeter-frame corner?

This calculator keeps frame intersections open and balances equal quantities on opposite sides, avoiding illogical corner crowding.

Does a living room require a central chandelier?

No. It is an architectural choice, not an automatic calculation result. Omit it, show it as decorative, or count it only with documented photometry.

Does higher wattage reduce spotlight quantity?

Only in estimated-lumen mode. With datasheet lumens entered, watts affect energy use while lumens determine brightness.

Does this replace DIALux?

No. It is a preliminary quantity and geometry check. Photometric uniformity and glare require IES/LDT data and a point calculation.