Supposing a time interval of 4 seconds, the light 41 will only listen for command messages in the first second, the light 42 in the period between the first and second second, the light 43 in the period between the second and third second, and the light 44 in the period between the third and fourth second. Each device will reduce power consumption by 75%. Since the four lights 41 to 44 are in the same group and perform a service on behalf of each other, whenever a command message is provided in the room for activating one of the lights in the group, at least one light will immediately react and become active (i.e. perform the service). This light may subsequently activate the other lights by forwarding the command message.
It is sometimes advantageous to allocate longer time periods to some devices and shorter time periods to other devices. For example, the processor of the mobile device 31 may be configured to determine the durations of the time periods of the schedule based on at least one of: energy consumption of the service-providing devices, spatial locations of the service-providing devices, spatial service-provisioning areas of the service-providing devices, usage of the service-providing devices, time required by the service-providing devices to enter and/or leave a standby mode, and identifiers of services provided by the service-providing devices.