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Lux & Lumens Calculator

Use our free Lux & Lumens Calculator to estimate the preliminary luminaire quantity needed for a room or project. Enter the room dimensions, choose the type of space, and add the delivered lumen output of one luminaire to calculate the required light output, whole-luminaire quantity and estimated maintained average illuminance.

Use the tool for homes, offices, retail spaces, showrooms, workshops, warehouses and other residential or commercial applications. Professional options allow project-specific utilization and maintenance factors, working-plane height and additional calculation context.

Saleh Deco Lighting Tool

Lux & Lumens Calculator

Estimate the preliminary luminaire quantity required to achieve a maintained average illuminance in a rectangular space. Start with simple planning assumptions, or enter project-specific utilization and maintenance factors.

Lumen methodMaintained average illuminanceMetric units
Calculation state loaded
Metres
Metres
Use complete-luminaire output, not LED-chip or source lumens.
A simplified starting point. Professionals should use luminaire/project photometric data where available.
Saleh Deco planning default for the selected activity.
Professional calculation options
Included in copied and printable reports; it does not affect the calculation.
Ratio used to estimate how much luminaire flux reaches the calculation plane. Use project/luminaire data where available.
Allowance for maintained performance over time.
Used for height context, room-index context and transfer to layout tools.
General horizontal plane
Used only for suitability warnings and layout-tool transfer; it does not change the lumen-method quantity.
Professional context
The lumen method estimates maintained average horizontal illuminance. Room index shown in the results assumes the luminaire plane is at ceiling height. Suspended luminaires and specification-critical projects should use project-specific photometric data.
Not calculated here
Uniformity, minimum illuminance, glare/UGR, vertical illuminance, point-by-point intensity and real product photometric distribution require photometric verification.

Calculation basis

Required luminaire output = area × target lux ÷ UF ÷ MF

Preliminary maintained-average estimate
This calculator determines target plane lumens, required initial luminaire output and a whole-luminaire quantity. Uniformity, glare, vertical illuminance and product-specific photometric distribution still require separate verification.

How to Use the Lux & Lumens Calculator

Estimate the maintained average light requirement first. If the project uses spotlights or downlights, transfer the calculated quantity into the Spotlight Layout Calculator to review spacing and arrangement.

1Select the space or task

Presets are Saleh Deco planning defaults, not universal regulatory requirements. Task presets such as desks and worktops apply to the named working plane, and you can replace the default target with a project-specific value.

2Enter delivered luminaire output

Use the rated output of the complete luminaire after optical losses. Do not enter wattage, LED-chip lumens or source lumens unless those are explicitly the delivered luminaire values.

3Understand the factors

Utilization factor estimates the proportion of luminaire flux reaching the calculation plane. Maintenance factor allows for maintained performance over time. The built-in UF choices are preliminary assumptions; project photometric data provides a better professional basis.

4Interpret whole-luminaire rounding

Luminaires are rounded up to whole units, so the estimated maintained average can exceed the target. A large surplus may indicate that a lower-output luminaire, dimming strategy or different layout deserves consideration.

5Continue to the layout tool when appropriate

If the project uses spotlights or downlights, transfer the quantity and room geometry to the Spotlight Layout Calculator. Other luminaire types may require a different arrangement method or product-specific photometric design.

Calculation method

Required initial luminaire output = area × target lux ÷ utilization factor ÷ maintenance factor.

Estimated maintained average = installed luminaire lumens × utilization factor × maintenance factor ÷ area.

Room index (context only) = length × width ÷ [height above working plane × (length + width)], assuming the luminaire plane is at ceiling height. The calculator does not automatically derive a product-specific utilization factor from room index.

What still requires photometric verification?
  • Uniformity, minimum illuminance and point-by-point distribution
  • Glare and visual comfort
  • Vertical illumination
  • High ceilings, narrow beams and specification-critical commercial applications
  • Suspended luminaire mounting planes that differ materially from the ceiling
  • Product IES/LDT distribution and real room reflectances


What are lux and lumens?

Lumens measure the total amount of visible light produced by a lamp or fitting. Lux measures how much of that light reaches a surface. One lux equals one lumen distributed over one square metre.

The number of fittings needed depends on the room area, desired lux level, lumen output per fitting, light distribution, ceiling height, room finishes, and maintenance conditions.

Read the Lux & Lumens Lighting Guide →

How accurate is the calculator?

The Saleh Deco Lux & Lumens Calculator provides a preliminary maintained-average lighting estimate using the lumen method. It uses room area, target illuminance, delivered luminaire output, utilization factor and maintenance factor to estimate the required whole-luminaire quantity.

Professional options also provide mounting-height and room-index context. These help review the calculation but do not replace product-specific photometric data. Actual results can vary with luminaire distribution, room reflectance, mounting position, furniture, spacing and installation conditions. Uniformity, glare, vertical illuminance and point-by-point performance require photometric verification.

Need help selecting a luminaire?

Browse Saleh Deco lighting categories or contact us with your room dimensions, ceiling height, intended use and target light level for help selecting suitable products for your project.

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