Comparison of LED and HPS Supplemental Light Quality on Greenhouse Tomato Production in Northern States during Winter Months

Plant production under controlled environments is rapidly expanding throughout the world and provides opportunity to meet the growing demands for locally grown fresh produce year-round. Tomato is one of the most economically important crops which requires Daily Light Integral (DLI) of 25 mol·m^‒2 ·d^‒1 for the optimal production, however, low DLI during winter months in northern states can significantly limit the production of tomatoes. The objectives of this study were to compare high-wire tomato (Solanum lycopersicum) production with and without supplemental lighting (control) during a fall to winter period and to evaluate the impact of light qualities and light sources [traditional overhead high-pressure sodium (HPS) lighting lamps vs. light-emitting diode (LED) intra-canopy lighting towers] on several production parameters for commercial greenhouse tomato production. Supplemental LED lighting treatments were provided as different combinations of blue (B) and red (R) spectra of Photosynthetically Photon Flux density (PPFD) at 230 μ mol s^-1 m^-2 in combination with far red (FR). Light treatments consisted of Blue (100B:60R:0FR), Red (0B:100R:0FR), 50% Far Red (0B:100R:50FR), 100% Far Red (0B:100R:100FR), and HPS and un-supplemented controls (0B:0R:0FR). Plant vegetative growth characteristics such as plant height, length of fully expanded leaves, and chlorophyll content were significantly increased with increasing FR and the values were similar to those from HPS treated plants. Total fruit yield per plant was increased by 300% in Red and by 275% in Blue compared to un-supplemented control. There was no significant difference between LED and HPS lightings in terms of total fruit yield with exceptions of Blue and in which fruit yield was reduced on an average by 5% compared to other LED treatments. The largest fruit clusters were obtained from plants grown with 100% Far Red, while un-supplemented control produced significantly smaller clusters. There was no difference in cluster size between other LED treatments and HPS. It is concluded that supplemental LED can produce equal or better greenhouse tomato yield and quality compared to HPS.