Lighting is one of the major energy end uses, which accounts for approximately 20-30% of electricity consumption in buildings. In fact, the fluorescent lamp is the most employed lamp in a lighting system for 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 reduce energy consumption in a lighting system, the electronic ballast has already been introduced for profit in terms of its peak demand reduction and energy conservation in the building. However, when the electronic ballast functions, harmonics will be generated. Hence, this paper investigates energy savings and 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 and compared with the fluorescent T8 lamp operating with a low watt loss electromagnetic ballast, which is also widely used. The obtained results are useful for the design and decision to install a fluorescent T5 lamp with electronic ballast in building lighting system to conserve energy and/or reduce energy consumption for the future of the country. (C) 2015 Elsevier B.V. All rights reserved.