A variation of the Rite of Three Rays has been used within the rituals of the Hermetic Order of the Golden Dawn for well over a Century. Anyone familiar with Golden Dawn Magick can verify this fact. It is also used as part of some of our rituals. Some of these are listed below:
Lesser Banishing Ritual of the Hexagram
The purpose of pointing out this fact is not to debate over who had what information first. Instead, what matters is that the technique, both as taught within the Pheryllt Text and Merlyn Series, works. It has been used by many groups both before and after the publication of the books.