To exempt light diffusers and lenses from the application of Sentence 3.1.5.1.(1), which would otherwise require the diffusers and lenses to be of noncombustible construction, and Sentences 3.1.13.2.(1) and 3.1.13.6.(5), which would otherwise require a lower maximum flame-spread rating, if certain conditions are met, on the basis that these building elements will not significantly contribute to the spread of flame.