I've learned that a Triac works as a switch for controlling AC current. Why not connecting the load (L1) and Triac in series? at the position of red arrow? My reason is that a small amount of current will always flows at the direction of green arrow. So, the load will always consume power and I don't think it is a good thing. Am I right?
Also, I don't understand the importance of DIAC. Would you give me a quick tip (information) about it?