The cactus Opuntia (genus Opuntia, subfamily Opuntioideae, family Cactaceae), commonly called nopal cactus or prickly pear, is characterized by its remarkable adaptation to arid and semi-arid climates. The stems of Opuntia are widely consumed as a vegetable in Mexico, Latin America, South Africa, and Mediterranean countries (Stintzing and Carle, 2005; Cruz-Hernandez and Paredes-López, 2010; El-Mostafa et al., 2014) as well as in Japan, where they are produced mainly in the Kasugai city, Aichi Prefecture. These plants are also used in some countries as remedies for a variety of health problems (El-Mostafa et al., 2014). For example, prickly pear is used as a folk medicine for burns, edema, and indigestion (Shetty et al., 2012). Opuntia plants are commonly grown in soil or pot culture. Major problems commonly encountered in growing vegetables in soil include soil-borne disease, salt accumulation, and difficulty in fertilizer management (Lakkireddy et al., 2012). In hydroponic culture, plants are grown using nutrient solution (water and fertilizer), with or without the use of an artificial medium. Soil-borne disease and weeds are eliminated in hydroponic culture because there is no soil and precise fertilizer management is also possible (Lakkireddy et al., 2012). Therefore, hydroponic culture provides advantages in the production of edible Opuntia, and we have shown that edible Opuntia can be grown by simple hydroponics culture (Horibe and Yamada, 2016). Edible Opuntia exhibit crassulacean acid metabolism (CAM), a CO2-concentrating mechanism that potentially leads to higher optimal temperatures for photosynthesis (Monson, 1989). CAM plants endure drought by anatomical modifications, such as thick cuticles and low stomatal frequency together with night-time CO2 uptake (Drennan and Nobel, 2000; Pimienta-Barrios et al., 2005), though daughter cladodes show C3 photosynthesis with daytime stomatal opening during the early stages of development (Osmond, 1978; Acevedo et al., 1983) and import water from mother cladodes (Pimienta-Barrios et al., 2005). Growth responses of Opuntia plants to temperature and CO2 concentration are well investigated (Gulmon and Bloom, 1979; North et al., 1995). Elevated CO2 concentrations increase the daily net CO2 uptake of cladodes and lead to increased biomass production (Cui et al., 1993; Nobel and Israel, 1994). Light is essential for plant growth, with both wavelength and intensity affecting plant growth and morphogenesis (Mortensen and Stromme, 1987; Yanagi et al., 2006). Studies have shown that light intensity affects the elongation growth of Opuntia daughter cladodes and the malate content of cladodes (Littlejohn et al., 1985; North et al., 1995). However, few studies have investigated the relationship between the light environment and growth of edible cacti as far as we searched (North et al., 1995). Understanding the relationship between environmental conditions and cladode growth is important for improving the production and quality of edible cacti. Here we cultivated Opuntia using h...