I find it interesting that the RFC had enough sets to loan them to the RE(SS) in June, 1915, though I gather it was only a few, and it doesn’t say for how long, although 1st Army had them for Loos. This does give credence to the idea that the RFC had switched to the Sterling in time for Loos.
Useful to know that the wavemeters above 300m are from Trench sets, and not RFC ones.
I note that 1 Squadron carried out trial work with Brock flares to identify infantry positions in August, 1915, which led to general issue to the infantry in November. WitA Vol 2 mentions ‘yellow smoke candles’ were used, unsuccessfully (i.e. no aircraft observer reported seeing any), at Loos. One wonder whether they were the same thing ? The IWM has a collection of such things but, seemingly, little information on them.