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To compare the efficacy and safety of low-level red light (LRL) in controlling myopia progression at 3 different powers: 0.37 mW, 0.60 mW, and 1.20 mW. Single-center, single-masked, randomized controlled trial. Two hundred children aged 6-15 with myopia of –0.50 diopter (D) or more and astigmatism of –2.50 D or less were enrolled from April to May 2022. Follow-up ended in December 2022. Participants were assigned randomly to 3 intervention groups and 1 control group (1:1:1:1). All participants wore single-vision spectacles. Moreover, the intervention group randomly received LRL at 3 different powers twice daily for 3 minutes per session, with a minimum 4-hour interval. Changes in spherical equivalent (SE), axial length (AL), and subfoveal choroidal thickness (SFCT) were measured. After 6 months, SE progression was significantly lower in the 0.37-mW group (0.01 D; 95% confidence interval [CI], –0.12 to 0.15), 0.60-mW group (–0.05 D; 95% CI, –0.18 to 0.07), and 1.20-mW group (0.16 D; 95% CI, 0.03 to 0.30) compared to the control group (–0.22 D; 95% CI, –0.50 to 0.30; adjusted P < 0.001 for all). AL changes in the 0.37-mW group (0.04 mm; 95% CI, –0.01 to 0.08), 0.60-mW group (0.00 mm; 95% CI, –0.05 to 0.05), and 1.20-mW group (–0.04 mm; 95% CI, –0.08 to 0.01) were significantly smaller than the control group (0.27 mm; 95% CI, 0.22 to 0.33; adjusted P < 0.001 for all). Similarly, increases in SFCT were significantly greater in the 0.37-mW group (22.63 μm; 95% CI, 12.13 to 33.34 μm), 0.60-mW group (36.17 μm; 95% CI, 24.37 to 48.25 μm), and 1.20-mW group (42.59 μm; 95% CI, 23.43 to 66.24 μm) than the control group (–5.07 μm; 95% CI, –10.32 to –0.13 μm; adjusted P < 0.001 for all). No adverse events were observed. LRL effectively controlled myopia progression at 0.37 mW, 0.60 mW, and 1.20 mW. Further research is required. The author(s) have no proprietary or commercial interest in any materials discussed in this article. [ABSTRACT FROM AUTHOR]