D5 apparently doesn’t yet recognize Arnold mesh light as a mesh light. It gives you a number of alternatives for that light but “mesh” is not one of them so all the emissive mesh lighting has to be controlled from the emissive material for the mesh object. The result is you kill the arnold mesh light and just tune the emissive material to get emissive lighting in D5. The lesson is, the control you had in max with your mesh light is lost in D5. FWIW