輝ける is seemingly the same as the potential form of 輝く, but actually they are different. 輝け is 已然形[いぜんけい] (the equivalent to the -ba conditional stem in Modern Japanese) of 輝く, and る is 連体形[れんたいけい] (the adnominal/attributive form) of a classical auxiliary verb り, which expresses continuous or perfective aspect. This form is still used in classical expressions, for instance 花咲ける騎士道 "the Japanese title of an old French movie 'Fanfan la Tulipe'" or 生ける屍 "living dead". (As you can see, 生ける is different from the potential form 生きられる. This 生け is 已然形 of a classical verb 生[い]く.)