Sentence:  Here, in the transept and choir, where the service was being held, one was conscious every moment of an increasing brightness; colours glowing vividly beneath the circular chandeliers, and the rows of small lights on the <WSD>choristers</WSD>' desks flashed and sparkled in front of the boys' faces, deep linen collars, and red neckbands. 
Meaning of the word marked with <WSD> tags:  A singer in a choir.