A customizable chamber spectral response is described which can be used at least to tailor chamber performance for wafer heating, wafer cooling, temperature measurement, and stray light. In one aspect, a system is described for processing a treatment object having a given emission spectrum at a treatment object temperature which causes the treatment object to produce a treatment object radiated energy. The chamber responds in a first way to the heating arrangement radiated energy and in a second way to the treatment object radiated energy that is incident thereon. The chamber may respond in the first way by reflecting the majority of the heat source radiated energy and in the second way by absorbing the majority of the treatment object radiated energy. Different portions of the chamber may be treated with selectively reflectivity based on design considerations to achieve objectives with respect to a particular chamber performance parameter.