A microscopic model for stretched exponential relaxation in glasses and other disordered systems is developed which exploits formal connections with optical phenomena in disordered systems. Two variations of the model are discussed. In the case of static disorder, contact is made with energy transfer in dilute systems; in the dynamic version of the theory, the connection is to the phenomenon of optical dephasing arising from interactions with two-level systems. In both versions, stretched exponential relaxation is related to singular behavior at low frequencies in the density of microscopic relaxation rates. Possible explanations for the singular behavior are assessed.