Light fixture mounting bracket assembly

An adjustable spring clamp comprising a mounting base, a pair of spaced-apart substantially parallel guide rails mounted on said mounting base, a displaceable spring clamp bracket retained between said pair of parallel guide rails for displacement therealong, said displaceable spring clamp bracket being secured to a displaceable base and held displaceably captive between said guide rails, said displaceable spring clamp bracket having a spring biased clamp arm secured to a torsion spring supported elevated from said mounting base by a vertical bridge support secured to said displaceable base, said spring biased clamp arm being biased in a downward direction towards an end of said mounting base by said torsion spring, spring elements between said displaceable base and said pair of parallel guide rails to urge a bottom surface of said displaceable base against a flat top surface of said mounting base, a retention formation provided in said bottom surface of said displaceable base for retention coupling with a selected one of spaced-apart retention projections immovably secured to said flat top surface of said mounting base to arrest said displaceable base at a selected location between said pair of spaced-apart guide rails to position said spring biased clamp arm at a desired location.