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Significant differences in light exposure were observed between school and summer in children, whereas activity and sleep were similar. Associations between parent and child behaviors suggest a potential mechanism for how myopia is transmitted from parents to children through patterns of environmental exposure, in addition to genetic factors.Objectively measured time outdoors, light exposure, activity, and sleep were examined in children during school and summer and assessed with eye growth. Associations between parent and child behaviors were evaluated.Children (aged 7.6 ± 1.8 years, n = 60) in Houston, TX, wore an actigraph device for three 2-week sessions (fall school, spring school, summer) to quantify time outdoors, light exposure, activity, and sleep. Cycloplegic autorefraction (WAM-5500; Grand-Seiko, Tokyo, Japan) and axial length (LenStar; Haag-Streit AG, Koeniz, Switzerland) were measured at baseline and 1 year. A subset of parents wore the device during their child's first 2-week session to compare behaviors (n = 33).Children spent 94.4 ± 30.6 minutes per day outdoors in spring, 110.6 ± 45.7 minutes in summer, and 72.2 ± 31.0 minutes in fall, with significant differences between sessions (P < .0001). Daily activity and sleep duration were similar across sessions (P = .73 and .06, respectively). Axial growth rate decreased with light exposure, but did not reach significance after adjusting for baseline axial length, age, sex, activity, and parental myopia (P = .073). Parent and child time outdoors and sleep duration were significantly correlated (P = .0002 and 0.026, respectively).Significant differences in light exposure were observed between school and summer, whereas activity and sleep were constant throughout the year. Children's behaviors were associated with their parent's behaviors, which may represent a modifiable component to potential environmental influences on eye growth. However, light exposure was not a significant environmental influence on axial growth in this study.