The Role of UV Radiation Added to LED Lighting System in Growth Control of African Violet (Saintpaulia ionantha Wendl.)

Light Emitting Diodes (LEDs) can be used as a tool to control the quality of plants in order to meet the requirements of the market by accurately schedule uniform flowering based on a predetermined market date. The aim of this study was to investigate the effect of different light qualities of red (R), blue (B), and UV-A (UV) provided by LEDs, and white light produced by fluorescent lamps (FL) on growth, morphology and flowering characteristics of African violet (Saintpaulia ionantha Wendl.). An experiment was conducted in controlled environment growth chambers at 25 °C. Three ratios of R:B (1:0, 3:1, 0:1) and FL (14 h/d) were used as all-day treatments and UV LED (2 h/d) was supplemented for three ratios of R:B (1:0, 3:1, 0:1) and FL (14 h/d) as end of day (EOD) treatment. Statistical analysis showed addition of B to light spectrum inhibited abnormal leaf growth and promoted compactness. Flowering under FL treatment was distinctly inferior as measured by the number of floral buds, full blooms and inflorescences. However, addition of EOD UV plus R3B1 contributed to higher production of floral buds and full blooms in a short period of time. Supplementing UV light to LED treatments resulted in accelerated leaf expansion. Generally, supplemental UV plus R or B was an acceptable energy-efficient alternative for improving quality of African violet. Vegetative and reproductive phase of Saintpaulia were a function of light quality which could assist the predictability of flowering time in controlled environment systems.