Background: The potential benefits and harms of different lighting in neonatal units have not been quantified. Objectives: To compare the effectiveness of cycled lighting (CL) (approximately 12 hours of light on and 12 hours of light off) with irregularly dimmed light (DL) or near darkness (ND) and with continuous bright light (CBL) on growth in preterm infants at three and six months of age. Search methods: We conducted electronic searches of the literature (in January 2013) of the Cochrane Central Register of Controlled Trials, Issue 12, 2012 (CENTRAL), MEDLINE, EMBASE, CINAHL and abstracts from Pediatric Academic Societies' annual meetings. We searched Controlled-trials.com and Clinicaltrials.gov for ongoing trials and abstracts from the Pediatric Academic Societies (PAS) Annual Meetings (2000 to 2013) using the Abstracts2view website on 10 May 2013. Selection criteria: Randomized or quasi-randomised trials of CL versus ND or CBL in preterm and low birth weight infants. Data collection and analysis: We performed data collection and analyses according to the methods of the Cochrane Neonatal Review Group. Main results: Six studies enrolling 424 infants compared CL versus ND (including one additional trial identified in this update that enrolled 37 infants). No study reported on weight at three or six months. In one study (n = 40), there was no statistically significant difference in weight at four months between the CL and ND groups. In another study (n = 62), the ratio of day-night activity prior to discharge favoured the CL group (mean difference (MD) 0.18, 95% confidence interval (CI) 0.17 to 0.19) indicating 18% more activity during the day than during the night in the CL group compared with the ND group. Two studies (n = 189) reported on retinopathy of prematurity (stage ≥ 3). There was no statistically significant difference between the CL and ND groups (typical risk ratio (RR) 0.53, 95% CI 0.25 to 1.11, I2 = 0%; typical risk difference (RD) -0.09, 95% CI -0.19 to 0.01, I2 = 0%). Two studies (n = 77) reported on length of hospital stay (days). There was a significant reduction in the length of stay between the CL and the ND groups favouring the CL group (MD -13 days, 95% CI -2 to -23). One study (n = 37) reported on less crying at 11 weeks' corrected age (CA) in the CL group compared with the ND group (MD -0.57 hours/24 hours, 95% CI -1.09 to -0.05).There was no heterogeneity for this outcome (I2 = 0%). Two studies enrolling 82 infants compared CL versus CBL. One study (n = 41) reported higher mean weight at three months' CA in infants cared for in the CL nursery (P value < 0.02) and lower mean number of hours spent awake in 24 hours at three months of age (P value < 0.005). One study (n = 41) reported shorter time on ventilator in the CL compared with the CBL group (MD -18.2 days, 95% CI -31.40 to -5.0). One study (n = 41) reported a shorter time to first oral feeding in the CL group (MD -6.8 days, 95% CI -13.29 to -0.31). For many outcomes, the trends favoured CL versus ND as well as CL versus CBL. We identified no safety issues. Authors' conclusions: Trials assessing the effect of CL have enrolled 506 infants. Trends for many outcomes favoured CL compared with ND and CL compared with CBL. The studies may have lacked significance due to a lack of statistical power. Future research should focus on comparing CL to ND.