CONCLUSIONS 57

In strawberries is it necessary to use supplemental lighting for 12 to 13 hours (Verheul et al., 2007). Longer lighting reduced the number of flowers. A day temperature of 18 °C and / or a night temperature o f 12 °C was the best to get flowers and also at the shortest time.

The positive influence of artificial lighting on plant growth, yield and quality of tomatoes (Demers et al., 1998a), cucumbers (Hao & Papadopoulos, 1999) and sweet pepper (Demers et al., 1998b) has been well studied. It is often assumed that an increment in light intensity results in the same yield increase. Indeed, yield of sweet pepper in the experimental greenhouse of the Agricultural University of Iceland at Reykir increased with light intensity (Stadler et al., 2010). However, with tomatoes, a higher light intensity resulted not (Stadler, 2012) or in only a slightly higher yield (Stadler, 2013a). First knowledge in growing berries at different light intensities is available: Also here had a higher light intensity (150 W/m2) a positive effect on marketable yield (Stadler, 2016). The harvest increased by 13-19 % when compared to the lower light intensity (100 W/m2). The higher yield was mainly attributed to a higher number of „extra class“ fruits. However, the experiments were conducted from January to May 2015 and from May to July 2015 and therefore are experiments during the darkest time in Iceland missing.

Incorporating lighting into a production strategy is an economic decision involving added costs versus potential returns. Therefore, the question arises whether these factors are leading to an appropriate yield of strawberries.

The objective of this study was to test if (1) the light intensity is affecting growth, yield and quality of different strawberry varieties, if (2) this parameter is converted efficiently into yield, and if (3) the profit margin can be improved by the chose of the light intensity and variety. This study should enable to strengthen the knowledge on the best method of growing strawberries and give strawberry growers advice how to improve their production by modifying the efficiency of strawberry production.