... cells of human body. The visibleblue light emitted by PDT can be perfectly absorbed by acne bacillus, and the ... and online service to teach you how to use the machine.After sales service:We have one year warranty, two ... any big fails, we will send you a new machine.2.Within one year, if you send back the ... 3. After one year, we offer to repair the machine, but we quire for the cost of the changed parts ...