this source for distribution around ring section 26 given the basic overall design of ring light guide 20 as shown in fig1 through 6b a number of variations in shape thickness light distribution and in mechanisms for tir frustration by different types of features 28 are possible fig7 8 9 10 and 11 a u2013 11 d show some of these variations from different views various types of features 28 can be formed on rear surface 30 for frustration of tir features 28 are non continuous and non planar that is are not flat smooth reflective surfaces or coatings instead features 28 are discrete elements such as indentations printed or otherwise applied patterns or protrusions that provide some type of light scattering surface discontinuities for frustrating tir at rear surface 30 in one embodiment features 28 can be a plurality of indented grooves or a sawtooth arrangement that effectively provides prisms for light redirection fig7 8 9 and 10 show an alternate embodiment in which features 28 present a generally sawtooth profile as shown in the perspective view of fig1 d alternately features 28 could have the shape of circularly cylindrical grooves as shown in fig1 a as well as using some other type of groove shape yet another configuration uses an array of discrete indentations or protrusions fig1 b for example shows features 28 as an array of ellipsoidal indentations formed into rear.