In order to improve the physiology of plants, this research evaluated the effect of high-intensity LED light (red, blue and green) on the following variables: germination (PG), hypocotyl length (HL), fresh (FW) and dry (DW) weight, in three types of lettuce seed (White Boston, Romana and Black Simpson). Exposure times with colour light were 12, 6 and 3h, with a complement of time for treatments with 6 and 3h of white LED light. We used a completely randomised design with four replications of 30 seeds. Treatments with green and red light to 12h had increases above 90% in HL against the control for the three varieties. The blue light treatment (3h) increased 23% in FW White Boston variety and the red light (3h) increased 14% the DW variable in Roman variety, compared to the control.  In this study, treatments with colour light presented results above the control; however, a treatment with a single type of light is not optimal to improve plant physiology. The physiological responses evaluated showed variation related to the genotype of seed and to the time of exposure to high-intensity LED light, so this type of light is a viable option for improving the physiology of plants.