A glint is brief and reflected light. It can be weak or intense. Although you can say just glint, people might say glint of light. "The plastic sign's glint made its words hard to see for a brief moment." "The car's side mirror flashed a glint of sunlight as the driver turned." A gleam is the quality of giving light. It can be reflected or directly from the sorce. It can be weak or intense. "The light bulb produced a constant gleam for the whole room." "The silver had a gleam." A shine is the quality of being bright. "That car had a lot of shine to it." (This sentence implies the car's paint reflected a lot of sunlight.) "The intense shine of the lighthouse reached for miles." As you probably noticed, some sentences can use any of the three words. "The sword's glint became visible as it turned." "The sword's gleam became visible as it turned." "The sword's shine became visible as it turned."