tLighting is one of the major energy end uses, which accounts for approximately 20–30% of electricityconsumption in buildings. In fact, the fluorescent lamp is the most employed lamp in a lighting systemfor both inside and outside the building. The ballast is one of the major components of fluorescent lamps;it exists commercially as an electromagnetic ballast, a low loss ballast and an electronic ballast. To reduceenergy consumption in a lighting system, the electronic ballast has already been introduced for profitin terms of its peak demand reduction and energy conservation in the building. However, when theelectronic ballast functions, harmonics will be generated. Hence, this paper investigates energy savingsand the generation of harmonics when using a fluorescent T5 lamp with electronic ballast in a building.The efficiency indices in terms of illumination, energy savings, and harmonics are also evaluated andcompared with the fluorescent T8 lamp operating with a low watt loss electromagnetic ballast, whichis also widely used. The obtained results are useful for the design and decision to install a fluorescentT5 lamp with electronic ballast in building lighting system to conserve energy and/or reduce energyconsumption for the future of the country.