The low-temperature threshold, evaluated over a 15-minute period, below which the module should raise a Threshold Crossing Alert, with at most one TCA sent per period; as with the high-threshold sibling, the UNITS clause (Celsius, 0.01 degree units) should be trusted over the description text's 'fahrenheit' wording. Admins use this to catch a transceiver running dangerously cold, for example in an unheated outdoor cabinet, which can also affect laser performance.