What is the Origin of Dim Light Melatonin Onset?

The term and its standardized measurement protocol were developed within the scientific disciplines of chronobiology and sleep medicine to provide an objective metric for the timing of the internal biological clock. Melatonin secretion, often referred to as the "hormone of darkness," serves as the primary, measurable output signal of the suprachiasmatic nucleus (SCN), the body's master pacemaker.

What is the Mechanism of Dim Light Melatonin Onset?

The suprachiasmatic nucleus receives photic input from specialized retinal ganglion cells via the retinohypothalamic tract, and as ambient light intensity falls below a specific threshold, the SCN disinhibits the pineal gland. This disinhibition triggers the enzymatic cascade that initiates the rapid synthesis and release of melatonin into the systemic circulation. The subsequent rise in melatonin acts on central receptors, promoting sleep propensity and synchronizing numerous physiological processes with the dark phase of the environment.

Dim Light Melatonin Onset

Meaning

Dim Light Melatonin Onset (DLMO) is the objective and precise physiological marker that indicates the exact time when the pineal gland’s secretion of the hormone melatonin begins its nocturnal rise under controlled, low-light conditions. Clinically, the DLMO is the most reliable phase marker for determining an individual’s intrinsic circadian rhythm, effectively marking the biological start of the subjective night. This measurement is indispensable for accurately diagnosing and strategically managing various circadian rhythm sleep-wake disorders.