In order to study the effect of the quality of different LED light spectra (90%Rþ10%B, 60%Rþ40%B and control)on photosynthetic parameters (photosynthetic rate (PG), Fv/Fm andΦPSII) of stomatal conductance, transpira-tion rate, carbohydrate, starch and chlorophyll index on cress (Lepidium Sativum), a pot experiment was conductedunder the greenhouse cultivation-without-soil (hydroponics) condition in the form of split plot based on acompletely randomized design with 6 replications. The results showed that the combined application of blue andred light spectra with different percentages had a positive and significant effect on all traits. The highest amountsof each of the photosynthetic parameters in the 60R:40B treatment were 12.4, 0.87, and 0.92 (μmol CO2m2s1),respectively, and the lowest amounts (19.6, 0.39, and 0.44 (μmol CO2m2s1)) were observed in the controltreatment. The highest amounts of stomatal conductance, carbohydrate and starch of leaves which were 0.3(cm.s2), 5.59 and 6.44 (mg.g-1 FW), respectively, were observed in the 90R: 10B treatment as a result of red lightincrease. Furthermore, in the control treatment, the light source of which was the natural sunlight, the lowestamounts of 0.11 (cm.s2), 1.98 and 1.09 (mg.g1FW) were observed. The highest transpiration rate (25/83(mol.m2.s1)) was observed in the 60R: 40B treatment which had experienced a significant increase compared tothe control light (sunlight) treatment and the lowest transpiration rate (5.5 (mol.m2.s1)) was in the control(sunlight) treatment. The chlorophyll index in the 60R: 40B treatment was 41.18, which showed a significantdifference from the other treatments (p0.01) and the lowest amount of 25.5 was detected in the controltreatment. As a result, it can be stated that the use of blue and red light spectra in combination with differentpercentages can have various positive effects on the growth and development of plants; therefore, the existence ofboth types of spectra is suggested. This technology means that a particular combination of LED light spectra can beuseful for a variety of commercial greenhouse products, especially the valuable ones

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