Fræðaþing landbúnaðarins - mar 2011, Page 181

MÁLSTOFA C – HEIMAFENGINN BAGGI | 181
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Christina Stadler1, Áslaug Helgadóttir2, Magnús Á. Ágústsson3, MonaAnitta
Riihimäki4

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
The extremely low natural light level is the major limiting factor for winter glasshouse
production in Iceland. Therefore, supplementary lighting is essential to maintain year
round vegetable production and this could replace imports from lower latitudes during
the winter months.
Previous experiments have shown that highpressure vapour sodium lamps (HPS)
used for interlighting produced a lot of heat and thus, resulting in burning on leaves
and fruits. The proportion of marketable yield on total yield of sweet pepper was
considerably decreased in interlighting systems compared to only top lighting,
because 2 % of the fruits were damaged from lighting and in addition blossom end rot
increased by 2 % (Stadleret al., 2010a). However, this could possible be counteracted
by using lamps for interlighting that are producing nearly no heat – which is the case
with “lightemitting diodes” (LEDs).
LEDs have been proposed as a possible light source for plant production systems (e.g.
Tamulaitis et al., 2005; Schuerger et al., 1997; Brown et al., 1995; Hoenecke et al.,
1992) and have attracted considerable interest in recent years among others, because
of their energysaving properties (Bula et al., 1991). This aspect seems to be
particularly interesting, because in Iceland the energy costs are a high percentage
(about 1/3; Stadler et al., 2010b) of the production costs and ways for decreasing
energy costs are quested.
The energy is cheaper during the night than during the day when time dependent
tariffs are selected (in sale during working days from 21.00  07.00 h and in
distribution all days from 23.00  07.00 h) and during weekends (in sale). The energy
price is highest from 01.11.  01.03. from 09.00  21.00 h in sale and from 07.00 
23.00 in distribution. Due to this “time dependent” tariffs the energy costs could be
decreased by lighting during the cheaper night tariff as well during whole weekends.
The objective of this study was to test if (1) HPS lamps can be replaced by LEDs and,
(2) decreasing energy costs by lighting at cheaper times will result in satisfactory
yield of sweet pepper and (3) how the choose of the light source and the lighting time
is economically effected.


An experiment with sweet pepper ( L. cv. Ferrari and cv. Viper) was
conducted in the experimental greenhouse of the Agricultural University of Iceland at
Reykir. Plants (two stems per plant, double rows) were transplanted at two stem
densities (Viper: 6 stems/m2 and Ferrari: 9 stems/m2) in four replicates. Sweet pepper