Retroreflexive material with alpha

How exactly does the alpha channel have to be set for the retroreflective material to work? Because it doesn't work for me with the alpha channel, but without it such material works properly (unfortunately I don't want it to be retroreflective everywhere). I couldn't find on the forum or in the lexicon what an alpha channel for retroreflective material should look like.

Thanks,

centipede

I figured it out! My mistake was that "retroreflexion" must be checked at the same time. Now it works great. The thread could be closed.