Rosa L. cultivars 'Korflapei' Frisco® and 'Bergme' Gabriella® were subjected to 12 supplementary PPFD levels, 0–174 μmol s-1 m-2, supplied by HPS-lamps for 20 h day-1 during two years, whenever the natural PPFD level inside the glasshouse dropped below 75 μmol s-1 m-2. The plants produced significantly more shoots, saleable flowers and first grade blooms, in the first and second year as well as in the summer and the winter with increasing supplementary light.
The supplementary lighting system was operating for about half the time.
Supplementary PPFD, 0–174 μmol s-1 m-2, linearly increased FW, DW and the uppermost five-leaflet-leaf area of the cut roses, and the number of petals per flower was enhanced till about 100 μmol s-1 m-2.
Supplementary light and rose yield and quality were generally linearly related, and the effects were consistent at all times of the year.
The biological efficiency (delta yield divided by delta mol) was as high or higher in the summer as in the winter, and the light conversion efficiency of Frisco® exceeded that of Gabriella® by a factor 1.6 on average.