What's meaning of the parameter "TransitionPeriod" in method "TransitionLampState" of the interface "org.allseen.LampState"

There is a method “TransitionLampState” in the interface “org.allseen.LampState”, and there is a parameter “TransitionPeriod” in this method, the parameter’s description is : “Time period (in ms) to transition over to new state”.

And I don’t know it’s meaning, transition over to new state will happen periodically, right? if so , does it take transition over to old state periodically also? how to understand this?

The TransitionPeriod is the time it takes to move from one state to the next. For example if you set the bulb to green, then set it to red with a TransitionPeriod of 2000ms it will take two seconds moving from green to red, and mix the colors in the meantime. Does that make sense?

Maybe I misunderstand this , i have been thinking this parameter stands for the event happens periodically. in fact it will move from green to red then finish this process.