Abstract: ObjectiveDaylight change rule and the influence of different light qualities on flowering and other physio-logical indicators of Bougainvillea spectabilis Willd.were studied to provide technical reference for B.spectabilis flowe-ring regulation.MethodWith Brilliant Red Bougainvillea as experimental material,physiological indicators such as net photosynthetic rate(Pn)and transpiration rate(Tr)were determined every hour on a summer day under natural lighting con-ditions in Nanning.The daily variation dynamic figure was drew.Treated by purple,red and white light qualities and natu-ral light,flower number,new branch length,chlorophyll content were determined after 45 d and 70 d of light irradiation. The effects of different light qualities on physiological indicators of B.spectabilis were analyzed.ResultDaily variation of Pnand Trpresented asymmetric bimodal curve with obvious midday depression phenomenon.After 45 days and 70 d of purple light treatment,the flower numbers were 171 and 23,increase rates were 612.50% and 2200.00% respectively.At the same time,the chlorophyll a content,chlorophyll b content,and chlorophyll a+b content were greatly higher than other groups.The effects of B.spectabilis flowers treated by these light qualities were as follows:purple light>red light>white light>natural light.After 45 days and 70 days light irradiation,new branch growth of B.spectabilis in all treatments were inhibited.In purple light treatment,after 45 d and 70 d,new branch lengths were 12.34 and 10.55 cm,growth rates were-32.34% and-6.88% respectively,which were largely lower than other groups.Therefore,the inhibition effects of purple light treatment was the most obvious.ConclusionUnder natural lighting conditions of summer day in Nanning,Brilliant Red Bougainvillea has obvious midday depression feature.Purple light is more favorable to the growth and the synthesis of chlorophyll.After using purple light to process B. spectabilis in production,the flower number at full-bloom stage in in-creased,flowering period is prolonged,new branch grows less and its ornamental value is promoted.