A rectangular luminaire includes a rectangular fixture defining at least one cavity having a plurality of light engines. A heat flange is disposed about a distal end region of the rectangular fixture and includes a hollow, generally pyramidal frustum shape with a generally rectangular cross-section. A distal-most end of the heat flange is configured to be disposed a distance D from a support surface when the rectangular fixture is received in a recess of the support surface, the distance D being greater than or equal to 0.4 times the fixture half-width W. Thermal energy is conductively transferred from the light engine, through the rectangular fixture, to the heat flange where the thermal energy is convectively transferred from the heat flange to surrounding air to create air currents flowing along the support surface thereby reducing the junction temperature.