Many manufacturers and distributors of LED tubes claim energy savings of 50% and more when replacing T8 fluorescent tubes with LED linear replacement lamps. Above, most distributors pretend that the same visual performance and comfort will be maintained after such replacement. Optical and electrical parameters of twelve commercially available LED tubes have been measured and compared and the evolution in time of these parameters has been monitored. The performance of these lamps with distinctly different luminance distributions is investigated. Additionally, a case study is presented in which the fluorescent lamps in a small office room were replaced by LED linear replacement lamps in order to compare the illuminance distribution on the work place. It has become clear that the impact of replacing a classical fluorescent tube by a linear LED lamp on the visual performance must not be underestimated.