Hopefully that cement is strong enough and not crumbly so you can actually set an anchor in it, but it might not be. Try a plastic anchor, and test the strength before hanging a light.

Your better option might be to build a light hanger out of PVC pipe or 2x4s, or get a 'portable clothes rack' from a department store. Those make acceptable light hangers if you make sure they are assembled securely.

Or maybe someone with masonry experience (bricked weed doesn't count hahaha) will chime in?