Coloured lights set in glass (7)
I believe the answer is:
signals
'coloured lights' is the definition.
The definition and answer can be both related to communication as well as being plural nouns.
Maybe there's an association between them I don't understand?
'set in glass' is the wordplay.
'set' is an anagram indicator (instruction to set the letters).
'in'+'glass'='inglass'
'inglass' with letters rearranged gives 'SIGNALS'.
Can you help me to learn more?
(Other definitions for signals that I've seen before include "Coded communications" , "Indications or gestures as information or warning" , "Flags, gestures" , "(Traffic) lights" , "Actions that encode messages" .)