*3.3. Irradiance Profile Measurements*

Irradiance measurements of the light fixtures were taken prior to the experiment using a spectral PAR meter (PG200N, UPRtek, Aachen, Germany) at night. Light intensity, spectral composition, and irradiance profiles (light distribution patterns) were measured and recorded at bench level under experimental conditions. The software package of the spectrometer (uSpectrum PC laboratory software) automatically calculated all electromagnetic parameters including photon flux density (PFD in µmol m−<sup>2</sup> s −1 ) and spectral irradiance (W m−<sup>2</sup> nm−<sup>1</sup> ) between 360 and 760 nm and photosynthetic photon flux density (PPFD in µmol m−<sup>2</sup> s −1 ) between 400 and 700 nm. During a sunny day, light transmission between 350 and 800 nm of the natural irradiance through the greenhouse glass was determined to be 28% (±5%) by comparing the output of the spectrometer inside the greenhouse with the output outside the greenhouse and resulted in a photon flux density of ~434 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> at bench level, which amounts to an approximate natural daily light integral of 3.9 mol m−<sup>2</sup> d <sup>−</sup><sup>1</sup> when combined with the weather recordings (Section 3.2). Light spectra and detailed spectral compositions of the supplemental lighting systems are depicted in Figure 4 and summarized in Table 1, respectively. Under each lighting system, the irradiance profiles within one square meter (representing the replicated experimental plots during the greenhouse experiment) were measured over a flat plane below the fixtures at intervals of 10 cm between 360 and 760 nm. Each measurement represents the spectral irradiance in W m−<sup>2</sup> nm−<sup>1</sup> and was replicated three times and averaged, leading to a total dataset of 100 measurements per square meter. These irradiance profiles are depicted in Figure 3.
