Provided is an in-store dual-mode communication system in which shelves are disposed within a commercial space. A server is coupled to the Internet and/or a wide-area network and is configured to send and receive communications. Also provided are light-based messaging units that are located on and/or attached to such shelves, each: 1) having a light source, 2) receiving a communication from the server, and 3) in response to receipt of such communication, turning the light source on and off so as to broadcast a digital message that was included within such communication, as a binary-encoded digital signal corresponding to on/off states of the light source. A user device: (i) receives, via its light sensor, and then decodes the binary-encoded digital signal from a light-based messaging unit in order to obtain the digital message that corresponds to it; and also (ii) communicates with the server via its wireless interface.