The structure and function of the human eye and the main visual defects are described. There is a detailed description and definition of lighting terminology and examples of equipment used to measure lighting levels at work. The chapter gives guidelines for the illumination of workplaces, including recommended illuminance levels and light distribution in workplaces and the use of color. Visual acuity is described as well as peripheral vision and perimetry. Visual fatigue and eyestrain are defined and described and methods for dealing with visual problems at work are given. Guidance for conducting lighting surveys is given. Psychological aspects of the lighting are discussed including seasonal affective disorder (SAD) and depression. Finally, the benefits of good lighting for workplace productivity and safety are discussed.