*3.2. Lighting Systems and Illumination Conditions*

Three different supplemental light sources ((1) fan-cooled light-emitting diode (LED) (SUNtec Technology, FUTURELED®, Berlin, Germany, dimensioning 47.5 <sup>×</sup> 21.5 <sup>×</sup> 19.5 cm<sup>3</sup> ), (2) high-pressure sodium (HPS) lamps (bulb: SON GreenPower CG T 400 W E40 1SL, PHILIPS, Hamburg, Germany; ballast: HST, SILL Leuchten®, Berlin, Germany, dimensioning 50 <sup>×</sup> <sup>30</sup> <sup>×</sup> 19 cm<sup>3</sup> ), and (3) fluorescent lamps (FL) (VENEDIG, Pracht®, Berlin, Germany, dimensioning 50 <sup>×</sup> <sup>50</sup> <sup>×</sup> 16 cm<sup>3</sup> )) were horizontally mounted onto given steel frames 1.40 m above greenhouse benches, resulting in distances between the bottom of the LED, HPS, and FL light sources and the greenhouse benches of 1.14, 1.13, and 1.09 m, respectively. Based on weather recordings from WetterKontor [62], plants were exposed to an average of 2.5 h of sunshine per day during the experiment. In addition to the natural sunlight, plants were subject to supplemental lighting from 6:00 a.m. to 8:00 p.m. for a photoperiod of 14 h per day during the greenhouse experiment. Plastic sheeting extending from above the light fixtures to below the greenhouse benches eliminated neighboring light pollution.
