PURPOSE: To obtain a light-diffusing resin compsn. excellent in flame retardance, light resistance, and moldability by compounding a styrenic resin with a halogen- contg. flame retardant, an ultraviolet absorber, a hindered amine stabilizer, and a light-diffusing agent.

CONSTITUTION: The resin compsn. contains 100 pts.wt. styrenic resin, 1-20 pts.wt. halogen-contg. flame retardant, 0.01-1 pt.wt. ultraviolet absorber, 0.01-1 pt.wt. hindered amine stabilizer, and 0.1-10 pts.wt. light-diffusing agent. A polystyrene resin is pref. as the styrenic resin in terms of cost. A pref. flame retardant is hexabromocyclododecane since it is effective even at a low amt. Examples of the ultraviolet absorber are a benzotriazole compd. and a benzophenone compd. Examples of the light-diffusing agent are glass, barium carbonate, zinc oxide, and a cross-linked polymer.