Successful lighting design begins with an assessment of several design issues to meet the occupants’ lighting needs, which depend on the tasks performed in the workspace. The lighting system should be designed to provide the quantity and quality of light responsive to those requirements. Several issues that should be considered are color, daylight availability, glare and light distribution. Retrofits that skip this assessment may perpetuate designs that have become inadequate because of workspace rearrangements or changing tasks.

It is important to recognize that people do not see absolute levels of illuminance, the amount of light shining on a surface. They see differences in luminance or brightness—the amount of light reflected back from the surface. The fundamental relationship between lighting and occupant tasks makes it essential that the lighting, task, and surrounding area be evaluated together. Although lighting retrofits are generally limited to the lighting equipment, good design should evaluate and modify work environments where appropriate. For example, a lighting redesign may reorient computer monitors away from windows or increase the contrast between tasks and their backgrounds.

Room dimensions and finishes also affect the required light output and thus the energy consumption of all interior lighting systems. As much as one-third of the energy use of a lighting system depends upon the surrounding interior features, such as the ceiling height, windows, and color and reflectivity of room surfaces and furnishings. Where possible, ensure that features that significantly enhance lighting levels, such as large windows and light-colored finishes, are utilized wherever possible. This helps minimize the required light output and therefore the energy consumption of the lighting system.

The same principals and guidance that apply to interior lighting are applicable to exterior lighting as well. Outdoor lighting that is designed and implemented properly should be cost effective, control light by directing it where needed; reduce glare and distribute illumination evenly; and reduce light trespass.