Since liquid crystals transmit {HEAD ~ only about 15%} of any incident light, the black light absorbing material facilitates observation and measurement of color changes in the liquid crystal material against {TAIL ~ a dark background} 
Since liquid crystals transmit { HEAD ~ only about 15 % } of any incident light , the black light absorbing material facilitates observation and measurement of color changes in the liquid crystal material against { TAIL ~ a dark background }
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