Sensor placement
Primary near-eye analysis with chest-level measurements as a complementary comparison
Near-eye measurements provide the primary estimates of light measured close to the eyes during wear; they do not directly measure retinal exposure. Chest measurements provide complementary evidence. The two sensor positions remain separate because they do not measure an interchangeable exposure, and combining them into one larger sample would not be scientifically justified.
Why the sensor positions stay separate
A sensor near the eyes more directly represents the light available to the eyes than a sensor worn on the chest. Body orientation, clothing, and local shading can affect the chest measurement differently. The size and direction of a position difference can also depend on the exposure measure, setting, participant, and day. Near-eye and chest measurements therefore are not treated as interchangeable, and similar estimates are not interpreted as evidence that the positions are equivalent.
The Descriptive results provide study-level context for the measurements recorded at the two positions.
How the positions are compared
Placement-specific models are fitted separately: near-eye models provide the primary result, while chest models provide the complementary result. A direct near-eye–chest comparison uses a common sample containing the same participants and participant-days at both positions. A participant-day means one participant’s record for one calendar day.
Repeated observations from the same participant and participant-day remain related in the analysis rather than being treated as independent. Results are reported in practical units with 95% confidence intervals (95% CIs). The relevant hypothesis report gives the exact numbers of participants, participant-days, observations, sites, and complete near-eye–chest pairs for the analysis it presents. Preparation 02: coverage and sample flow explains how measurement coverage and availability determine those samples.
What sleep-period measurements represent
During sleep, the devices are not worn at their nominal near-eye and chest positions. Values recorded during the sleep period therefore describe the bedside sleep environment. They are not interpreted as light measured on the body at the usual waking sensor positions.