Background: Poor sleep is common among older adults at risk for dementia and may be due to circadian dysregulation. Light is the most important external stimulus to the circadian clock and bright light therapy (BLT) has been used for >20 years to help realign circadian rhythms. However, the ability of field methods (e.g., actigraphy) to accurately determine the type and intensity of light is unknown.

Objective: We examined the ability of the MotionWatch8 (MW8) light sensor to determine: 1) light versus dark, 2) electrical light versus daylight, and 3) device-based BLT versus light which was not BLT.

Methods: We tested the MW8 under 17 daily light scenarios. Light exposure data was collected for 5 minutes during each scenario. Concurrently, we measured light exposure using the LT40 Light Meter, a sensitive measure of light intensity. We then developed individual cut-points using receiver operator characteristics analyses to determine optimal MW8 cut-points for 1) light versus dark; 2) electrical light versus daylight; and 3) light from a BLT box versus light which was not BLT. Bland-Altman plots tested the precision of the MW8 compared to the LT40.

Results: The MW8 accurately discriminated light versus dark (>32 lux), and electrical light versus daylight (<323 lux). However, the MW8 had poor accuracy for 1) discriminating BLT from light which was not BLT; and 2) low precision compared to the LT40.

Conclusion: The MW8 appears to be able to discern light versus dark and electrical light versus daylight; however, there remains a need for accurate field methods capable of measuring light exposure.


CAMNTECH COMMENT: The light sensor incorporated into the MW8 provides an indication of luminous light intensity (lux) with peak wavelength closely matching the human eye response. In practice, commercial lux meters will have correction factors to adjust for different light sources due to their different spectral characteristics. We posit that a further experiment comparing two or three different specialist lux meters would yield differing light intensity results for the same light sources. Such specialist light meters also incorporate cosine correction filters which are many times the physical size of the MW8.


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Journal: Journal of Alzheimer's Disease Reports.(Preprint):1-9

Keywords: bright light therapy, Dementia, Light, light exposure, luxometer, older adults, Sleep,

Applications: Light Exposure,

CamNtech Reference: M21033

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