The southern African geophyte Lachenalia with an enormous number of species and cultivars is nowadays a commercially important plant material. There is a need for research on the optimization of growing conditions to obtain a satisfactory visual quality of potted plants, which may boost its production on the international ornamental market. Our research can be considered as an innovative study on supplemental irradiation with various light spectra in relation to flower quality of Lachenalia spp. The main objective was to examine the usefulness of LED lighting in extending the length of the natural day to a 16/8 h photoperiod in order to control the development of Lachenalia ‘Rupert’ inflorescence during greenhouse cultivation in Central-European winter time. Three light treatments were applied with red (660 nm) and blue (440 nm) light in different ratios: 100% red (100/0), 90% red mixed with 10% blue (90/10) and 80% red with 20% blue (80/20). The PPFD at the plant leaf level was approx. 150 μmol m-2 s−1. The most favourable spectrum, 90/10, induced the longest inflorescences characterized by the highest stem diameter with simultaneously the highest number of florets. Additionally, blue light increased the anthocyanin content in the corolla by about 35%, compared with plants exposed to 100% red light and non-irradiated ones (control plants). This first study on the wavelength ratios is aimed to increase the production quality of Lachenalia and indicates the need for continuation.