The roof light system is composed by a roof unit (10), a light conduit (70) and a diffuser unit (80). A ventilation device has a ventilation tube (60) is separate and detached from the light conduit (70). The first end (60a) of the ventilation tube is connected with the roof unit (10) and the second end (60b) is positioned at a distance from the diffuser unit (80). The ventilation device may additionally have a branch tube (160).