The Radiance Technique® is the original, intact science of Real Reiki®, Authentic Reiki®. The word "reiki" is a generic term which can be used for anything at all. Real Reiki® and Authentic Reiki® are service marks which were registered decades ago to denote and distinguish the intact science of energy from a plethora of personal methods being called "reiki." The service marks are a consumer protection, guaranteeing the student or recipient of Authentic Reiki®, Real Reiki® is in fact receiving the application of transcendental, harmless, whole energy.
The intact science which was called "reiki" in Japan was brought to the United States by Hawayo Takata. She chose one, and only one, person -- Dr. Barbara Ray -- to whom to pass all the Keys of the complete science. After Mrs. Takata's death, some people began to make things up based on partial study with Mrs. Takata and called them "reiki." However, those people never learned the complete system from Mrs. Takata, and so they could not teach others to teach, no matter what they claimed. Today, four decades after Mrs. Takata chose Dr. Barbara Ray as her successor, often people who claim to do "reiki" things do not even know they learned some generic thing called "reiki" from someone else who never had access to the intact system at all.
There are no other "versions" of the original Reiki taught by Hawayo Takata. It would be as if someone wanted to make lights come on in their house and randomly ran wires without connecting them to the electricity: without the correct procedures and connection to the electrical grid, that person would not be able to turn on a light switch and have the lights come on. That person could attach a light switch to the wall, and could flip the switch making it look the same as any other switch. However, without the correct wiring, it simply does not turn on the lights. Authorized Instructors are correctly trained and "connected" to the intact science of Authentic Reiki® so that when they do the "wiring" (metaphorically speaking), the connection is there, reliably, every time.