2017 ASHS Annual Conference

For indoor growing of vegetables by home consumers, light quantity and quality are limiting factors. The objective was to evaluate plant performance of ‘Red Salad Bowl’ lettuce in a simulated indoor environment grown with four commercially-available light-emitting diode (LED) or fluorescent fixtures, and one of the LED fixtures at four light levels. In the first experiment, we tested four white light sources that included 4000 K or 5000 K LED, or 4100 or 6500 K tubular fluorescents, at 120 µmol·m-2·s-1 for 12 hours per day (5.2 mol·m-2.d-1). Lettuce had greater biomass when grown under LEDs compared with fluorescents, but greater anthocyanin levels and nitrate content under fluorescent light. In the second experiment, a 4000 K LED light source provided four light levels: 37, 52, 85, or 150 µmol·m-2·s-1 for 12 hours per day (1.6, 2.2, 3.7, or 6.5 mol·m-2.d-1). As light level increased, plants had shorter leaves, greater biomass, and higher chlorophyll and anthocyanin content. Light levels of 3.7 and 6.5 mol.m-2.d-1 resulted in the same fresh weight and chlorophyll content, but the highest light level resulted in higher dry weight, more compact growth (decreased leaf length), and increased anthocyanin content. In a simulated home consumer environment, any of the four white LED or fluorescent fixtures tested could be used to grow lettuce, with a minimum of 3.7 mol.m-2.d-1, although higher light would be desirable. A daily light integral of 3.7 mol.m-2.d-1 could be provided, for example, with one 4000 K LED bulb per square foot run for 15 hours at a minimum 4-in height, at a cost of $0.01 to $0.02 per square foot per day for electricity at $0.05 to $0.15 per kWh and $25 for the light fixture per square foot.