Sentence:  With fears that draping normal Christmas fairy lights through the tree's aluminium branches would cause a short circuit, the trees were lit from below by a rotating <WSD>colour wheel</WSD> divided into wedge-shaped segments of variously coloured plastic. 
Meaning of the word marked with <WSD> tags:  A device that emits varying colours of (light) by the use of a (wheel), commonly used to illuminate (Christmas trees).