实现楼道间照明灯的方便控制，一个照明灯，在楼上和楼下各有一个（闭合式）开关控制。开关的闭合并不直接决定灯的亮灭，而开关状态的改变才是决定灯亮灭的关键。即不管两个开关当前的状态如何，只要有一个开关状态发声变化，都会使照明灯在打亮或者熄灭两种状态间切换。

-Achieve inter-corridor lighting control convenience, a lamp, upstairs and downstairs each have a (closed) switch. Switch is closed does not directly determine the bright lights off, change the switching state is the key to determine the lamp on or off. That no matter how the current state of the two switches, as long as there is a switch status change sound, will make playing in the bright lights off or switch between the two states.