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Coefficient of utilization, lumen method

Definition

The lumen method is an indoor lighting calculation methodology that allows a quick assessment of the number of luminaires necessary to achieve a given average illuminance level, or alternatively the average illuminance level that will be achieved for a given number of luminaires. It is valid for empty rectangular rooms with simple 3-surface diffuse reflectance’s for ceiling, wall and floor.

Introduction

When an electric lamp is turned on it emits light and it is possible to quantify the amount of light by measuring it, the result being given in the units of lumens. In itself this is a useful piece of information, but what would be more useful would be to have a method of converting this into a measure of the amount of light that would be received onto a desk from one or more luminaires, or alternatively the number of luminaires necessary to achieve a given quantity of light on the desk. This calculation is known as the lumen method.