The use of supplemental lighting systems is increasing as more growers become interested in shortening the time needed for their crops to reach maturity, and/or in continuous plant production throughout the winter season. The installation and operation of supplemental lighting systems can add significantly to the overall energy requirement of a greenhouse operation. Obviously, the selection of energy efficient luminaires is an important design consideration. In addition, a high degree of light uniformity is required for consistent plant production throughout the growing area. Sometimes, different design criteria are used to characterize the light distribution in plant production facilities. Several of these design criteria are discussed in this study. Other times, the design of supplemental lighting systems for plant production facilities is optimized with the help of sophisticated computer software programs. Depending on the dimensions and characteristics of the plant production area, the available luminaire mounting height, the average height of the crop, and the number and placement of the particular luminaires selected, the software calculates the resulting light intensity and uniformity. Or, based on the desired light intensity, it calculates the required number and placement of the selected luminaires. In this study, the usefulness of light uniformity criteria and design software is demonstrated. These design tools can help improve or evaluate light uniformity either during the design phase, or after installation of a lighting system.