Embodiments described herein generally relate to apparatus for processing substrates. The apparatus generally include a process chamber having a substrate support therein. A plurality of lamps are positioned to provide radiant energy through an optically transparent window to a substrate positioned on the substrate support. The plurality of lamps are positioned in a lamp housing. A cooling channel is formed in the lamp housing. A surface of the lamp housing is spaced a distance from the optically transparent window to form a gap therebetween. The gap functions as a fluid channel and is adapted to contain a fluid therein to facilitate cooling of the optically transparent window. Turbulence inducing features, such as openings, formed in the surface of the lamp housing induce a turbulent flow of the cooling fluid, thus improving heat transfer between the optically transparent window and the lamp housing.