An LED light source with a lens is mounted to a light housing. The lens is sealed to form an encapsulated atmosphere about the LED. The housing has a cylinder and a divider between the cylinder and the LED. A slidable and sealed piston in the cylinder creates an air chamber between its upper surface and the divider and a lower surface of the piston is exposed to air pressure of the outer atmosphere. A conduit is formed through the divider to interconnect the encapsulated atmosphere with the air chamber in the cylinder. LED heat causes the pressure of the encapsulated atmosphere to increase, and it flows through the conduit to press against the piston. This piston slides to create a larger air chamber to equal the increased pressure of the encapsulated atmosphere to the pressure of the outside atmosphere. The reverse occurs when the LED cools.