The instant invention relates to a thermoplastic polymer composition useful in greenhouse films to enhance plant growth or in general bio-mass production. Further aspects of the invention are a process for enhancing plant growth in greenhouses by incorporating a photoactive additive together with light stabilizers into the greenhouse film and the use of the condensation product of dialkylamino benzaldehyde and barbituric acid together with light stabilizers as a plant growth enhancing additive in polymeric greenhouse films.