Light sources are labeled with an output rating in lumens. For example, a T12 40-watt fluorescent lamp may have a rating of 3050 lumens. Similarly, a light fixture's output can be expressed in lumens. Light Level Light intensity measured on a plane at a specific location is called illuminance.
Illuminance is measured in footcandles, which are workplane lumens per square foot.
You can measure illuminance using a light meter located on the work surface where tasks are performed. Using simple arithmetic and manufacturers' photometric data, you can predict illuminance for a defined space. Brightness Another measurement of light is luminance, sometimes called brightness. Therefore, the amount of light delivered into the space and the reflectance of the surfaces in the space affects your ability to see. The Illuminating Engineering Society of North America has developed a procedure for determining the appropriate average light level for a particular space.