See, don't equivocate "Light" with other forms of light as we know it. The Guardians energy known as "Light" has a tangible and physical aspect to it. It is apparent it isn't just photons and electromagnetic waves. A solar flare is superheated material and radiation. Since people don't get sick by hanging with guardians (as far as we know) then it isn't radiation either. So the "Light" from Guardians is different.