An on line free setting method for setting an operating parameter of a lighting device is disclosed. The method involves using a user interface APP comprising at least one free setting algorithm preloaded in a mobile device to transform a user's setting decision into an operating variable of an operating parameter of the lighting device, wherein the user interface APP is operable on a touch screen panel of the mobile device; wherein the free setting algorithm is a capacity scale simulation process implemented by operating a visual configuration of a free setting operator interacting with a capacity scale simulator and an indicator of the capacity operating rate to facilitate making the user's setting decision, wherein the operating parameter is used for controlling various functional performances of the lighting device including light intensity, light color temperature, delay time and detection sensitivity.