This paper presents the results of an experimental analysis conducted on two 800 mm long and φ = 250 mm tubular light pipes installed in the Technical Physics Laboratory, Faculty of Architecture of Pescara. They consist of a clear polycarbonate dome installed on the roof top, which captures sunlight and skylight and redirect it into the pipe itself, which transmits it away, through multiple reflections, to the light output device, called “diffuser”, which distributes light inside the room. The experimental analysis was carried out in order to determine the influence of two types of diffusers on inside distribution of light. Both the considered diffusers are polycarbonate made; the first one presents a prismatic geometry and it is able to get quite a uniform spatial light distribution, while the second one is characterized by a radial geometry and it is totally see-through in the centre, giving a smaller light absorption but a less uniform distribution of light. Several tests were conducted in both configurations and the obtained data were compared each to the other. In order to limit the influence of boundary walls reflections a horizontal work plane was considered 700 mm distant from the diffuser and black sheets of drawing paper (ρ = 5,5 %) were mounted around the diffuser itself. The results allow to describe what the differences between illuminance values in the two considered configurations and to do useful considerations about how spatial distribution of light incoming from light pipes is conditioned by diffusers characteristics.