Results showed that monochromatic light could affect testosterone secretion (Table 3). During the early stage, plasma testos-
terone concentrations were higher in GL than in RL and WL (7 d: 41.52 to 47.28%; 21 d: 34.8 to 45.73%, P < 0.05), but no significant difference was observed between GL and BL (P > 0.05).