0023-6152

AA00697606

1911214

The aim of this study was to analyze the fundamental lighting characteristics (spectrum distribution and light intensity) of a low–light LED unit and its effect on gas exchange in strawberry leaves. This unit was newly developed to provide low–cost supplemental lighting for greenhouses. The low–light LED unit was made using 24 LED module chips, each of which were 1 m in length and 43.2W. The electricity consumption of this unit was only 55% of that of the high–light LED previously reported by Hidaka et al. (2013). The spectrum characteristics of low–light LED were measured using a portable spectro–radiometer. The photosynthetic photon flux density (PPFD) was measured using a photon sensor, and its distribution was measured at five different heights from a reference plane (110 cm × 150 cm). Gas exchange in strawberry leaves under low–light LED (Low LED treatment) supplemental lighting and no lighting (Control treatment) were measured using a leaf chamber system. The results demonstrated that the spectrum distribution patterns of the low–light LED and the high–light LED were similar; we found that the relative light intensity of both LEDs peaked once near a wavelength of 450 nm and again near a wavelength of 550 nm. The PPFD and its horizontal distribution showed that, as the height of the light source increased, the PPFD and lighting regions decreased and increased, respectively. On the other hand, as the height of 20 cm, PPFD under supplemental lighting with the low–light LED increased by 2.1 times than natural condition. As a result, stomatal conductance and transpiration rate increased by 1.5 times and 1.2 times, respectively; further photosynthetic rate increased by 2.2 times. Thus, the low–light LED was demonstrated to have suitable wavelength for crop production. Furthermore, applying supplemental lighting with the low–light LED significantly improved light intensity and accelerated photosynthesis in strawberry.