A plant growth lighting fixture includes a lighting fixture main body having a light exit surface, a light source held on the lighting fixture main body, and a reflective-type circularly polarizing plate that selectively reflects circularly polarized light having a particular rotational direction in a particular wavelength range. The reflective-type circularly polarizing plate has a support and a circularly polarized light reflecting layer held on the support. The lighting fixture main body has a holding mechanism for detachably mounting the reflective-type circularly polarizing plate with a main surface of the reflective-type circularly polarizing plate facing the light exit surface.