This read-write value sets the low warning threshold for whichever DDM parameter the row's swDdmThresholdType identifies, encoded as a DisplayString because the value is a floating-point number, and sits above the corresponding alarm level to give earlier notice. An admin uses it to get a heads-up on a slowly degrading optic before it crosses into alarm territory. For example, setting swDdmLowWarning to "-22.0" on an rxPower row surfaces a fiber that is losing margin well before the -30 dBm alarm threshold is reached.