Fræðaþing landbúnaðarins - mar. 2011, Blaðsíða 185

MÁLSTOFA C – HEIMAFENGINN BAGGI | 185
(Demers et al, 1998a). Dorais (2003) reported chlorosis on tomato after only several
days with more than 17 h or continuous supplemental light. In contrast, tomato plants
showed nearly no negative symptoms under almost 24 hours of natural sunlight in
Finland. Therefore, on the one hand the quality of light (natural / artificial light) and
on the other hand the duration of the supplemental light seems to be the crucial factor
for positive / negative effects. Thus, the duration of the continuous lighting during
weekends may be decisive for the lower yields, because after changing to the normal
lighting time plants adapted again in their yield.
When supplemental light was provided from 04  22 h compared to 23  17 h
Gunnlaugsson & Adalsteinsson (2003) observed 12 % higher yields of tomatoes, this
compensated for higher electricity costs of 11 % at normal lighting times. Hence, the
authors concluded that therefore it is not necessary to adjust the lighting time for
tomatoes to the tariffs of electricity. This was confirmed in the present experiment
with sweet pepper.


With LED interlighting it was possible to decrease energy costs by 25 %, but a 20 %
lower yield of sweet pepper resulted after consideration of the revenues in a clearly
profit loss. Also, 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.


We thank Samband garðyrkjubænda and Framleiðnisjóður landbúnaðarins for their
support of this research, Gavita, Frjó and Ljósin í bænum for supply of the lighting
system as well as LbhÍ staff for their assistance.


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