The lamps on a phone device can be lit in a variety of different lighting modes. Unlike ringing patterns, lamp modes are more uniform across phone sets of different vendors. A common set of lamp modes is defined by Win32 Telephony. A lamp identified by its lamp/button identifier can be lit in a given lamp mode. A lamp can also be queried for its current lamp mode.
The lamp functions are TSPI_phoneSetLamp, which lights a lamp on a specified open phone device in a given lamp lighting mode, and TSPI_phoneGetLamp, which returns the current lamp mode of the specified lamp.
When a lamp mode of a phone device is changed, the service provider sends a PHONE_STATUS message to the tapi32.dll callback function to notify it about the state change. Parameters to this message provide an indication of the change.