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Recessed light fixtures can create a variety of problems in insulated ceilings or attics. These perforated metal cans, operating at close to 200°F, act like tiny chimneys, drawing moist indoor air up into the ceiling cavity (see Figure 1). In cold weather, the moisture condenses against the roof sheathing, causing a buildup of water or frost (which eventually melts into water). The wet sheathing can get blackened from mold. In cathedral ceilings, the water often drips back to the house, staining the ceiling and finishes. Recessed lights also hurt the performance of attic insulation. The hot fixtures cause convective loops that seriously degrade the effective R-value of the insulation surrounding the fixture. This problem is not well documented, but research at Oak