Portable light towers are a significant source of glare to motorists entering a work zone. Although existing research has evaluated the effect of light tower orientation on visibility and glare, the effects of factors like mounting height, offset distance from the roadway, and number of light towers in the work zone on visual performance and discomfort glare are not known. Understanding these relationships can help to develop illumination guidelines for work zones that can reduce glare for drivers. The goal of this project was to understand the effect of mounting height, offset distance to the roadway, and number of light towers in the work zone on drivers’ visual performance and discomfort glare. Participants drove through a realistic work zone and evaluated portable light towers with varying mounting heights, offset distances, and number of light towers. Results showed that the mounting height and offset distances play a critical role in affecting the driver’s visual performance and discomfort glare rating. Portable light towers, irrespective of wattage and lumen output, at lower than a mounting height of 20 feet and closer to the roadway (in travel lanes than in the shoulder) result in decreasing drivers’ visual performance and increasing their discomfort glare. Portable light towers should be mounted at a height of at least 20 feet, and balloon light towers with higher wattage (4,000 watts and greater) and lumen output (400,000 lumens and greater) should be located at an offset distance of at least 10 feet from the roadway.