Three hyacinth cultivars were forced under fluorescent lamps which emitted white, blue, green, yellow and red light. The plants started flowering in the first decade of February. The forcing period for two cultivars, ‘Anna Marie’ and ‘Blue Star’, was shortest under lamps emitting red light. The cultivar ‘White Pearl’ flowered equally early under lamps emitting red, white and blue light. The impact of light colour (wavelength) on the leaf greenness index (SPAD) was demonstrated. The photosynthetic activity of leaves was dependent on the cultivar. It was related both to the net rate of photosynthesis and the photosynthetic efficiency. Specific leaf area (SLA) also depended on the cultivar. The level of SLA was related to the rate of photosynthesis and its efficiency. SLA was highest in all cultivars under green and yellow colour light. The chlorophyll content in the fresh and dry weight of leaves was highest under yellow light lamps.

Three cultivars of Hyacinthus orientalis L. were forced under artificial light using fluorescent lamps emitting white, blue, green, yellow and red light. Quantum irradiance was determined as 12.5 and 25 µmol m-2 s-1. Day length was 12 and six hours, respectively. Daily light integral was 0.54 mol m-2. A significant effect of light colour on flowering date and plant quality was observed. Plants forced in blue and red light were the first to flower. Plants exposed to red light formed longer inflorescences. Plants forced under lamps emitting blue light formed shorter, more rigid flower shoots with shorter leaves. There were no significant differences between plants grown under 25 μmol m-2 s-1 of quantum irradiance for six hours per day and plants grown under light with a quantum irradiance of 12.5 μmol m-2 s-1 for 12 hours per day. This means that the light-dosing variant did not exert any effect on the growth and flowering of hyacinths.

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