In this paper, a hollow light guide with edge-lit LED sources has been proposed to simultaneously resolve the issues of weight, uniformity, and efficiency.  The major approach is to modulate the LED luminous intensity profile by a ring of parabolic surface with continuously varied focal length.  The modulated light emitting profile directly makes up sufficient uniformity on the planar surface, and extra components are not required. 
LED
In this paper, a hollow light guide with edge-lit LED sources has been proposed to simultaneously resolve the issues of weight, uniformity, and efficiency.  The major approach is to modulate the LED luminous intensity profile by a ring of parabolic surface with continuously varied focal length.  The modulated light emitting profile directly makes up sufficient uniformity on the planar surface, and extra components are not required. 
LED