Many manufacturers and distributors of LED tubes claim energy savings of 50% and more when replacing T8 fluorescent tubes with linear LED replacement lamps. Most distributors even pretend that the same visual performance and comfort will be maintained after such a replacement. Optical and electrical parameters of twelve commercially available linear LED tubes have been determined and the evolution in time of these parameters has been monitored. 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 plane, the glare perception and the overall visual appreciation. It has become clear that a one-to-one replacement of a classical fluorescent tube by a linear LED lamp has severe consequences on the lighting quality.