Lumen Calculator (Lumen to Lux to Candela)

Lumens measure total light output; lux measures how much lands on a surface.

How the Math Works

The Lumen Calculator uses the fundamental relationship between luminous flux and illuminance: lux equals lumens divided by area. Luminous flux (measured in lumens) represents the total perceived light emitted by a source, while illuminance (measured in lux) indicates how much of that light spreads over a specific surface area. When you divide the total light output by the area it covers, you determine the light intensity per square meter. For example, a 1000-lumen bulb shining evenly over 10 square meters produces 100 lux of illuminance.

Practical Applications

To use this calculator, simply enter the total luminous flux in lumens and the area over which the light spreads in square meters. The calculator instantly computes the illuminance value in lux. This is particularly useful for lighting designers who need to ensure adequate light levels in rooms, for photographers determining how much light reaches their subject, or for architects planning daylighting strategies. The tool works in reverse too — you can calculate the required area for a given light output and desired illuminance level.

Day-to-Day Use

Understanding lux levels helps you create the right lighting environment for any situation. You can verify if your living room receives enough natural light for your comfort, determine if your bedroom lighting is sufficient for reading, or check whether your workspace meets recommended illumination standards. Many public spaces publish their lighting levels in lux — museums often use around 50 lux for sensitive artifacts, while supermarkets typically provide 300-500 lux for clear product visibility. This knowledge empowers you to make informed decisions about lighting purchases and room layouts.

Worked example

800 lm over 10 m² → 80 lux.

FAQ