6 CONCLUSIONS

6 CONCLUSIONS

The very low reduction in energy costs by lighting during nights and weekends was accompanied by a higher loss in yield. From the economic side it seems to be recommended to provide light at normal times with HPS lamps.

However, by providing light at normal times, growers could decrease the energy costs by about 6 % in using light with 100 J/cm2/cluster and 100 J/cm2 for plant maintenance. After consideration of the revenues this resulted in a clearly profit benefit from about 10 % compared to the traditional lighting system. Therefore, growers are better off to decrease the lighting time during the early stage after transplanting and also turning lights of at high natural light levels.

Growers should pay attention to possible reduction in their production costs for tomatoes other than energy costs.