Acta Hortic. 1271. ISHS 2020. DOI 10.17660/ActaHortic.2020.1271.14 XXX IHC – Proc. III Int. Symp. on Innovation and New Technologies in Protected Cultivation Eds.: F. Boyaci et al. 101 Effects of different artificial light spectra on growth of Lettuce in a continuous light plant factory system M. Khoramtabrizi 1 , S. Aliniaeifard 2,a and Gh. Chegini 1 1 Department of Agro Technology, Aburaihan campus, University of Tehran, Iran; 2 Department of Horticulture, Aburaihan campus, University of Tehran, Iran. Abstract Nowadays plant factory systems have been proposed as a viable alternative to increase productivity per unit area of cultivated land by extending crop production in vertical dimension along with efficient resource consumption, without environmental pollution. To investigate productivity of lettuce plants in plant factory systems, plants were cultivated in closed three layers vertical cultivation systems where they exposed to continuous lighting of LEDs (light-emitting diode). The LED light wavelengths were in the range of 660 to 680, 420 to 440 nm and 730 to 750 nm for red, blue and far-red lights, respectively. Plants were grown under three lightning spectra: full red (R), 75% red and 25% blue (RB), and 50% red, 25% blue and 25% far-red (RBF), provided continuous light with 250 µmol m -2 s -1 PPFD and 21±1°C. Growing of the plants under continuous light resulted in some necrotic spot on the plant leaves exposed to R and RB treatments. Highest fresh and dry weights and also leaf area were obtained in full R treatment. However, Plant under this treatment showed deformed leaves (strong epinasty). RBF treatment resulted in very tall plants with limited number of necrotic spots than the R treatment. Keywords: continuous light, LED lighting, lettuce, light quality, plant factory INTRODUCTION It is estimated that urban population will have been surpassing six billion by 2050 compared to the initial population of 3.4 billion in 2010, over 70% increase (Rosenzweig et al., 2010). Concurrent with dwindling number of farmers as well as climate change issue, a novel idea of growing crops in order to feed the world emerged: plant factory with artificial lighting (PFAL) (Kozai and Niu, 2016). PFALs as a vital component to ensure a sustainable and healthy future, offer a host of benefits, including high productivity per unit area, high resource use efficiency and pesticide-free crops, as compared to conventional systems (Despommier, 2011). Nowadays thanks to technological advances, light-emitting diodes (LEDs), can deliver better light quality in terms of color rendering and accurate wavelength while also providing an energy efficient advantage over conventional artificial light sources. LEDs are promising technology for the PFALs industry that have provided numerous benefits over their traditional counterparts, including compact size, durability, long lifetime, and low heat output. More importantly, LEDs are offered capability of light wavelength manipulation for desired specific spectra unlike HID and incandescent lamps. It is well known that light consist of three relevant parameters including quality (spectral distribution), intensity and duration, has different effects on plant growth. The length of light and dark periods regulates vegetative and flowering in broad range of plants which are sensitive to photoperiod. There are tremendous variables that have a huge impact on consistently production of high quality crops, including spatial uniformity of light, air temperature, humidity, CO2 concentration, nutrition solution, etc. Among which light is not only the most important environmental factor affecting the growth and development of plants (Han et al., 2015), but also it can be boosted quantity of plants production. Recent developments in regarding light quality have led to believe that red (R) and blue (B) light are wavebands of interest to scientist a E-mail: aliniaeifard@ut.ac.ir