A tubular skylight for lighting rooms with natural light, comprising a tubular body with a reflective inner surface which leads into a room and has, at its external end, a natural light collector assembly and, at its internal end, a light diffuser. The collector assembly comprises, inside an optically transparent dome arranged so as to close the tubular body, a mirror-finished body which is substantially shaped like a cylindrical band with mirror-finished inner and outer surfaces. The axial width of the band-like body varies gradually from a minimum-width point to a maximum-width point, which lie diametrically to each other. It is also possible to provide a cylindrical refracting body that surrounds said mirror.