A lighting fixture includes a frame, one or more LED light sources to emit radiation, control circuitry to receive AC power and control the one or more LED light sources, and a coolant pipe to carry a fluid coolant. The lighting fixture further includes a tube and end caps that together form an enclosed cavity to contain the frame, the LED light sources, and the control circuitry. In example implementations, the tube does not physically contact the frame, the LED light sources, and the control circuitry. The cavity may further contain air, gas, or vacuum that forms a thermal barrier between the tube and the LED light sources to reduce heat dissipation from the LED light sources to the environment. The tube may further enable the lighting fixture to be rotatably and/or translationally adjustable relative to a support structure after installation in a close proximity grow system.