Investigation of a scanning laser projector as an energy-efficient light source in plant production

<p>The energy costs for artificial lighting in plant factories are very high, but may be decreased by introducing more efficient light sources. Light absorption in plants takes place in the order of a femtosecond, while the chemical reactions for carbon fixation of 5 milliseconds are limiting the processing of photons by the photosystems. In this article, the Showwx^™ scanning laser projector (0.1 W) was tested as an energy-efficient lighting source for cultivating lettuce (Lactuca sativa L. cv. Frillice). This projector uses a mirror where three laser beams are combined and scanned in diverging bi-directional pattern. The average pixel scan time is 20 nanoseconds, while the scanning of the complete projection takes 17 milliseconds. The laser projector was used for artificial lighting of lettuce seedlings (1 week after sowing) and bigger crops (4 weeks after sowing). The light levels were very low (10-20 μmol m^-2 s^-1) in order to adapt the illumination area of the laser projector to the plant area. A fluorescent lamp (8 W) was used as a reference light source and was mounted on a height, where an equal PPFD was measured at plant height. No differences in relative growth rate were observed in both experiments between the two light sources. A higher final fresh weight was observed for the seedlings illuminated using the scanning laser projector. This particular projector was considered to be not suitable as an artificial light source, but an improved scanning laser projector (with higher laser powers) provides opportunities to improve light efficiency and decrease production costs greatly.