A plant lighting device (1), constructed at an indoor planting (9), includes an illumination module (11) and a power module (12). The illumination module (11) includes an assembly seat (111), and an illumination unit (112) including a plurality of light emitting elements (113) that emit light toward at least one plant (9) when powered up. The power module (12), mounted on the assembly seat (11), includes a power input line (121), a ring transformer module (122) connected to the power input line (121) and receiving an external power to perform power transformation, and a power output line (123) connected to the ring transformer module (122) and the illumination unit (112). The ring transformer module (122) includes a ring core (124), a primary coil (125) winding around the ring core (124) and connected to the power input line (121), and a secondary coil (126) winding around the ring core (124) and forming magnetic coupling with the primary coil (125) to output a non-harmonic alternating current power to the power output line (123).
