The illuminance levels set by the guide follow the CIBSE Code for lighting. The guide sets out recommended illuminance for different types of work, and sets the minimum light levels necessary for Illuminance of the task and Illuminance ratio.
Different activities require different levels of light. In general, the more detailed the task, the greater amount of light is required. A process control room should be lit at an illuminance of 300 lux, a corridor or walkway may only require 50 lux, whilst studying a detailed technical drawing may require 750 lux.
The illuminance ratio recognises the importance of the relationship between the lighting in working areas and adjacent areas. Sudden change of illumination or harsh contrast in illumination are the most common cause of hazards and visual discomfort. Changes in lighting should be made gradual where possible.
