An apparatus for regulating the radiation of light and/or heat by the use of slats which are suitable for placing under a roof constructions, such as a greenhouse roof, in which the slats 140 are supported at or adjacent each end by a pair of laterally spaced apart connecting cords 136,137. These cords form the sole suspension for the slats and are mounted, at their upper ends, on a combined tilting and carrier means 102,107,108,115. Drive 128 is provided for the combined carrier and tilting means so that the latter impart a movement from which the tilting movement of the suspended slats is directly derived. It is also possible for the slats to be drawn back by movement of runners 134,135 on the combined carrier and tilting means.
