A b s t r a c tThe pot cultivar of Chrysanthemum x grandiflorum 'Leticia Time Yellow' was cultivated and stored in a growth room under fluorescent light of white, blue, green, yellow and red colour. Quantum irradiance was 30 μmol· m . The colour of light exerted a significant influence on the opening of closed inflorescence buds and on post-harvest longevity of pot chrysanthemums grown earlier in an unheated plastic tunnel. Under florescent lamps emitting blue light at a wavelength of 400-580 nm, inflorescence buds opened and coloured the earliest. The number of developed flower heads was the greatest under blue and white light. Flower heads developing in blue light were bigger than flower heads developing in white and green light. In red light at a wavelength of 600-700 nm, plants flowered latest and they produced the smallest flower heads. Post-harvest longevity was preserved longest in chrysanthemums kept under blue, white and green light. In red and yellow light, the flowers were overblown earliest.

Four narcissus cultivars were forced under artificial light using fluorescent lamps which emitted white (307 -770 nm), blue (393 -580 nm), red (540 -760 nm), yellow (450 -750 nm), or green (387 -680 nm) light. The photosynthetic photon flux density was 12.5 µmol m -2 s -1 , with a 6 h photoperiod. Light colour (wavelength) had no significant effect on flowering date, or on the number of flowers collected (P < 0.05). Narcissus bulbs exposed to blue light (393 -580 nm) formed shorter, more rigid shoots of lower weight with 13 -40% shorter leaves.

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.

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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.