Fræðaþing landbúnaðarins - Mar 2011, Page 184

| FRÆÐAÞING LANDBÚNAÐARINS 8, 2011184
Compared to the normal lighting regime, with LED interlighting a profit loss of 15 
25 % and with lighting during night and weekend from 15  20 % was calculated
(Tab. 2).

 Relative energy costs, revenues of sweet pepper and profit at different
lighting regimes.
   

(costs for distribution (subsidised) and for sale)

100

72  78

98  100

Viper, 6 stems/m2
Ferrari, 9 stems/m2

100
100

76
83

90
87
(revenues  energy costs)
Viper, 6 stems/m2
Ferrari, 9 stems/m2

100
100

76
87

86
80


Marketable yield of sweet pepper was decreased by LEDs for interlighting compared
to HPS for interlighting by 20 % when HPS top lighting was used additionally. Also
Trouwborst et al. (2010) reported that 38 % LED interlighting in addition to 62 %
HPS top lighting in cucumbers did not increase total biomass or fruit production.
However for comparison the authors have used 100 % HPS top lighting.
Generally, there is a deficit in experiments with two different light sources together in
combination, whereas experiments with the comparison of different light sources have
been conducted more often. Using LEDs compared to other light sources resulted in
both positive and negative results: E.g. plant biomass of sweet pepper seedlings was
significantly reduced under LEDs compared to metal halide lamps (Brown et al.,
1995). In contrast, growth of lettuce plants maintained under LEDs was after 21 days
equivalent to that reported in the literature for plants grown for the same time under
coolwhite fluorescent and incandescent radiation sources (Bula et al., 1991). Massa
et al. (2008) assume that it seems likely that LEDs will soon approach and surpass in
their efficiency of traditional lighting sources.
The sweet pepper plants tolerated supplemental lighting during whole weekends and
nights. However yield was decreased compared to the normal lighting time from 04 
22 h. Did plants receive not only during weekends but continuously (24 h) light, it
resulted in lower yields of sweet pepper and leaf deformation (Demers et al., 1998b).
The authors discussed that it may be an opportunity to provide continuous light for a
few weeks to improve growth and yields. If the continuous lighting during weekends
is considered as such a system, then this could not be confirmed in the present
experiment.
Tomatoes exposed to continuous light started developing leaf chlorosis after seven
weeks, while during the first 5  7 weeks tomato plants grown under continuous light
had better growth and higher yields than plants receiving 14 h supplemental light