Arthur Light has already been referenced on the show, back in season 2 episode The Man Under The Hood, so he certainly exists within the shows universe. He is mentioned as the creator of the weapon that produces energy blasts they use against Slade, and its also said he worked at S.T.A.R Labs but was fired because he went crazy. In the comics, he becomes the villain Doctor Light, whose mind is wiped at one point by the Justice League and he plans revenge on them, starting with Green Arrow. He possesses a genius-level intellect, and also the ability to control light to his advantage, such as creating force fields, energy blasts, and becoming invisible. These metahuman sounding abilities wouldnt be out of place on The Flash, and the character is one who could certainly crossover between both shows. After all, would they have mentioned him if he wasnt going to appear at some point?