LEDs devices with different light intensities
All of the combined LEDs had the uniform spectra of red and white, and were designed by Beihang University, China. The spectral distribution of the red (peak at
658 nm) and white (from 350 nm to 750 nm) light (300 W) were measured using a spectroradiometer (Avaspec-2048–UA, Avantes B.V., Netherlands). In each treatment, photosynthetic photon flux density (PPFD) of the red and white LEDs were equal and the LED array was supplied with 50% red light intensity and 50% white light intensity (R:W = 1:1). PPFD was measured using a quantum sensor (Li-250, Li-Cor, USA). The parameters of the light intensity in each treatment are shown in Fig 1. All of the treatments were placed in a culture room and were arranged in as separate plots with different light intensities.