The precise quantification of the intensity of visible light exposure received by the eye, expressed in lux, which is a key metric in chronobiology and sleep medicine. This measurement is critical because the non-visual effects of light on the circadian system are dose-dependent, requiring a specific minimum intensity for phase shifting or melatonin suppression. Clinically, it is used to prescribe the exact Light Dose necessary for an Early Morning Light Protocol or to identify insufficient daytime light exposure that contributes to Systemic Rhythm Misalignment. Accurate measurement ensures the therapeutic efficacy of light interventions.
Origin
The term combines the environmental stimulus “Light” and the quantitative term “Dose” with “Lux,” the international system (SI) unit of illuminance, which is derived from the Latin word for light. Its application in the clinical setting arose from research defining the irradiance thresholds required to affect the Hypothalamic Suprachiasmatic Nucleus (SCN). This led to a paradigm shift, recognizing that light must be treated as a measurable, therapeutic input, much like a pharmaceutical agent.
Mechanism
Lux measures the luminous flux incident on a surface, directly correlating to the amount of light stimulating the intrinsically photosensitive Retinal Ganglion Cells (ipRGCs). These cells require a significantly higher light intensity than rods and cones to trigger their response. By measuring the Light Dose in lux, the Clinical Translator can ensure that the environmental or device-delivered light is sufficient to maximally suppress melatonin secretion or phase shift the SCN. This ensures the intended biological effect, such as Cognitive Alertness Induction, is achieved.
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