IES specifies the recommended footcandle levels for different tasks for indoor
and outdoor lighting. Let's look at these recommendations and how to
calculate the appropriate light level for an application. Keep in mind that certain
situations may call for higher levels than IES recommends. A work area for
visually impaired workers, as an example.
Indoor IES light levels
require a four-step process.
- The first step is to define the visual task. The important thing is the task
contrast and size. This should be the most important task performed in a given
- The second step is to define the illuminance category, based on the visual
- The third step is to decide the illuminance range based on the previous
- And finally, the fourth step is to establish the illuminance target value
based on age, accuracy and room or task surface reflectances. The fourth step uses
weighting factors to decide the target value. Check the IES handbook to figure
in these weighting factors.