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