Lumens Calculator

How It Works

Our lumens calculator estimates the appropriate brightness requirements for a space, as well as the ideal colour temperature based on lighting needs and lux requirements.

A number of factors influence how many lumens are required to achieve the ideal brightness for a space. The square footage, and ceiling height, of a room are perhaps the most important variables, with larger rooms needing more lumens to achieve the same level of brightness. However, wall colour also influences lumen requirements. This is because lighter walls reflect more light than darker walls, so rooms with lighter walls appear brighter, even if they have the same lumen output.

If you would like to discover the ideal range of Kelvin values (colour temperature for your lighting), reference your Lux Requirement result, and check which colour temperature it aligns with on the graph below (the Kruithof curve).

First, this calculator determines the square footage of the room you'd like to light. Then it takes wall colour reflectance into consideration before outputting the total recommended lumens and foot candles for your lighting project. See below for a breakdown of how this lumens calculator works, along with the formulas it uses.

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Formulas for Lumens Calculator

Formula for the floor surface area that the light would need to cover. Ceiling height is a separate variable.

A

(length * width)

By taking the R, G and B values of an RGB colour code, we can get the reflectance of a wall. This reflectance is then accounted for in the final calculation of recommended lumens. The LRV result will be a number between 0 and 1, but shown as a percentage in the output field. The relationship between the reflectance of a surface, and the surface's equivalent RGB value, is as follows.

Reflectance (LRV)

(0.2126 * R + 0.7152 * G + 0.0722 * B)

255

100

Calculating the wall adjustment is necessary when accounting for reflectance of wall colour. Though similar to reflectance, it is not the same. The purpose of calculating "wall colour adjustment" is to determine the additional lumens per square foot needed based on a wall colour's reflectance. Rooms with darker wall colours absorb more light, so they require more lumens to achieve the desired lighting levels than a wall of a lighter colour. The value of the "wall colour adjustment" represents the additional foot candles needed, ranging from 0 (for highly reflective walls) to 10 (for very dark walls). By subtracting the brightness ratio from 1, we obtain the darkness ratio. Then we multiply it by 10 to obtain the additional lumens per square foot needed to compensate for the light absorbed by the walls.

Brightness

(0.2126 * R + 0.7152 * G + 0.0722 * B)

Wall Colour Adjustment

(1 - brightness)

255

10

The purpose of calculating a "ceiling height adjustment" is to determine the additional lumens per square foot needed based on a ceiling's height. This formula uses logarithmic scaling to help account for the fact that higher ceilings require more light for adequate illumination of a space. The increase in lumens as the ceiling height increases is not linear, it is actually exponential, and using a logarithmic formula is essential to demonstrate this.

Ceiling Height Adjustment

(log(ceiling height + 2.0)) * 20

20

Lumens

sqft

(FC + wall adjustment + ceiling adjustment)

Lux Requirement

(Lumens)

(10.76 * Square Feet)