Abstract: This invention relates to height adjustable extensions of in-ground containers for embedded container light supports in airport runways. The apparatus has a first and second telescoping tube, each having a wall terminating in a flange. The flange on its upper end is for the reception of a light fixture, and the flange at the bottom end has bolt holes registering with the flange on the upper end of the in-ground container. There are a plurality of tapped bores in the wall of the outer tube. Set screws in the tapped bores are adapted to bear on the inner tube. The method of extending the height of the lighting fixture container comprises these steps: providing the apparatus as described above, positioning the telescoping tubes at a required height position; tightening the set screws to temporarily preserve the height position; pouring cementitious material around the positioned tubes; and allowing the cementitious material to set to hold said tubes in place.