Objective: To analyze near work illuminance patterns on school days and weekends among third and fourth grade primary school students by using objectively monitored data, and to examine the associations of the duration of near work under different illuminance levels and time weighted average near work illuminance with screening myopia. Methods: From April to June 2024, students from grades 3 and 4 in two primary schools in Jiading District, Shanghai were selected as study subjects by using stratified random cluster sampling method. Continuous objective monitoring of near work behavior was conducted for 7 days while information from uncorrected visual acuity and refractive assessment was collected, and an online questionnaire survey was administered to their parents. Valid samples comprised 372 students on school days and 292 on weekends. Welch s t test was used to compare differences in the duration of near work under different illuminance levels between the screening myopia and non-myopia groups. Multivariable binary Logistic regression analysis was employed to assess the association between the duration of near work under different illuminance levels and screening myopia. Restricted cubic spline (RCS) model was used to explore the nonlinear association between time weighted average near work illuminance with 60 cm and screening myopia, and the critical thresholds identified by the RCS model were used to categorize illuminance levels for subsequent Logistic regression analyses. Results: Objective monitoring of near work behavior showed that the duration of near work in the low illuminance range of [0,125)lx was significantly longer on weekends[(4.12±2.21)h] than on school days [(2.42±1.22)h]. Multivariate Logistic regression analysis revealed that only on school days, each additional hour of near work duration in the [0,125)lx ( OR =1.56, 95% CI =1.23-1.98) and ≥1 000 lx range ( OR =5.92, 95% CI =1.48-23.73) were significantly associated with higher odds of screening myopia(both P < 0.05). RCS plot showed that on school days, time weighted average near work illuminance with 60 cm had a non-linear association with screening myopia ( P non-linear <0.05). On weekends, no significant association was found between near work illuminance indicators and screening myopia (all P >0.05). Conclusions Primary school students engage in near work for considerable durations in insufficient lighting environments on both school days and weekends. Increased duration of near work in overly dim or bright environments on school days may increase the risk of screening myopia.