Fræðaþing landbúnaðarins - mar. 2011, Blaðsíða 334

| FRÆÐAÞING LANDBÚNAÐARINS 8, 2011334

Christina Stadler 1, Erlingur Brynjúlfsson 2





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. Highpressure sodium lamps are the most commonly
used type of light source in greenhouse production. However, in recent years light
emitting diodes (LEDs) have attracted considerable interest for supplemental lighting
of vegetables.
Growth of lettuce plants maintained under LEDs was after 21 days equivalent to what
is reported in the literature for plants grown for the same time under coolwhite
fluorescent and incandescent radiation sources (Bula et al., 1991). Also, Kim et al.
(2004) measured similar shoot fresh weigh of salad plants, 28 days after planting,
under red and blue LEDs compared to coolwhite fluorescent lamps at same PPF
between 400  700 nm.
However, salad seedlings developed extended hypocotyls and elongated cotyledons
when grown under highintensity redemitting LEDs as the sole source of
supplemental lighting. This extension and elongation was prevented when the red
LED radiation was supplemented with a bluephoton flux level of at least
15 µmol/m2/s (Hoenecke et al, 1992), whereas the addition of 10 % blue light to salad
plants was not sufficient to achieve the same growth of plants grown under coolwhite
fluorescent lamps (Yorio et al., 2001). As revealed in previous studies, a combination
of red (600  700 nm) and blue (400  500 nm) light has proven to be an effective
lighting source for e.g. spinach, radish and salad (Kim et al., 2004; Yorio et al., 2001).
Pinho et al. stated 2007 that there have not been sufficient reports of studies using
LEDs as supplemental lighting in real greenhouse conditions for salad growth.
Therefore, the objective of this study was to test (1) if salad can be grown under LEDs
instead of commonly used highpressure sodium lamps and (2) if energysavings are
going along with an appropriate yield.


An experiment with salad (L. cv. Grand Rapids) was conducted in the
experimental greenhouse of the Agricultural University of Iceland at Reykir. In
1.25 m x 1.00 m big boxes, filled with a mixture of peat (¾) and pumice (¼), salad
was planted in distances of 25 cm x 25 cm (16 plants/m2) in four repetitions. The
plants were either lightened with high pressure sodium lamps (400 W, Super Agro,
Gan 4550 AL, Voltage: 220/230 V) or LEDs (100 W, blue (¼): 462 nm, red (¾): 660
nm) for 16 hours (from 05.0021.00 h). The lamps were placed at 2.65 m / 1.0 m
(HPS / LED) above the plant canopy. The temperature was adjusted to 21 °C / 15 °C
(day / night) and it was watered as needed. The inner six plants were harvested after