Firstly, how does the wand ignite if he wasn’t using it?
Secondly, why is Harry tried for use of the Patronus but not for the use of the Lumos?
Do these two questions answer each other? The Trace may not be on wandless magic; the trace is on the magical signature from when a spell is produced from a wand. (And Dobby deliberately ‘forges’ a magical signature onto his spell to incriminate Harry; Dobby’s other uses of magic therefore go unnoticed) The Lumos was Harry’s desperation forcing a use of wandless magic; it wasn’t a regular spell.