AIM: To investigate the effects of spectral composition and light intensity on natural refractive development in guinea pigs. METHODS: A total of 124 pigmented guinea pigs (2-week-old) were randomly assigned to three groups at high (Hi; 4000 lx), medium (Me; 400 lx) and low (Lo; 50 lx) light intensities under a 12:12 light/dark cycle for 6wk. Each group was subdivided into subgroups with the following spectra: broad spectrum Solux halogen light (BS), 600 nm above-filtered continuous spectrum (600F), 530 nm above-filtered continuous spectrum (530F), and 480 nm above-filtered continuous spectrum (480F; HiBS: n=10, Hi600F: n=10, Hi530F: n=10, Hi480F: n=10, MeBS: n=10, Me600F: n=10, Me530F: n=10, Me480F: n=10, LoBS: n=11, Lo600F: n=12, Lo530F: n=10, Lo480F: n=11). Refractive error, corneal curvature radius, and axial dimensions were determined by cycloplegic retinoscopy, photokeratometry, and A-scan ultrasonography before and after 2, 4, and 6wk of treatment. Average changes from both eyes in the ocular parameters and refractive error were compared among different subgroups. RESULTS: After 6wk of exposure, high-intensity lighting enhanced hyperopic shift; medium- and low-intensity lighting enhanced myopic shift (P<0.05). Under the same spectrum, axial increase was larger in the low light intensity group than in the medium and high light intensity groups (HiBS: 0.65±0.02 mm, MeBS: 0.67±0.01 mm, LoBS: 0.82±0.02 mm; Hi600F: 0.64±0.02 mm, Me600F: 0.67±0.01 mm, Lo600F: 0.81±0.01 mm; Hi530F: 0.64±0.02 mm, Me530F: 0.67±0.01 mm, Lo530F: 0.73±0.02 mm; Hi480F: 0.64±0.01 mm, Me480F: 0.66±0.01 mm, Lo480F: 0.72±0.02 mm; P<0.05). Under 400 lx, there was a faster axial increase in the MeBS group than in the Me480F group (P<0.05). Under 50 lx, axial length changes were significantly larger in LoBS and Lo600F than in Lo530F and Lo480F (P<0.01). CONCLUSION: Under high-intensity lighting, high light intensity rather than spectrum distributions that inhibits axial increase. Under medium- and low-intensity lighting, filtering out the long wavelength inhibits axial growth in juvenile guinea pigs.