The study findings revealed that the study groups did not differ significantly from each other regarding the means of calorie intake and the pattern of weight gain. Nonetheless, the pretest-posttest mean difference of body weight in the experimental group was significantly greater than the control group (P = 0.04). These findings denote that cyclical lighting at the NICU can promote preterm neonates’ growth and weight gain.
The findings showed that during the first days of the study, the neonates experienced weight loss. The amount of weight loss during these days in the experimental group was less than the control group. However, the neonates started to gain weight from the fifth day. In the control group, not only the rate of weight loss during the first four days was faster, but also the rate of weight gain during the remaining days was slower than the experimental group. Consequently, the difference between the groups regarding the pretest-posttest mean difference of body weight became statistically significant. The insignificant difference between the groups regarding the pretest and posttest mean values of body weight can be attributed to different factors such as the short course of the study, small sample size, and neonates’ sleep disturbances due to mothers or healthcare professionals’ frequent visits and frequent removal of the linen cover of their incubators.
Taheri et al. (2005) also studied the effects of cyclical lighting on weight gain among 66 preterm neonates and found that there was no significant difference between the pretest and the posttest values of body weight neither in the control nor the experimental groups. Nevertheless, pretest-posttest mean difference of body weight in their experimental group was significantly greater than their control group (P = 0.041) (
13). Our findings were also similar to the findings reported by Taheri et al. (2005) probably due to factors such as the short course of both studies (ten and five days, respectively) and relatively small sample size of the studies.
The results of other studies in this area are different from or in contrary to ours. For instance, Kennedy et al. (1997) found that neither cyclical lighting nor continuous darkness were effective in promoting preterm neonates’ weight gain. A probable explanation for such contrary findings may be the differences in the gestational and the postnatal ages of the participants of these two studies. Besides, Kennedy et al. (1997) used eye covers for the neonates in their target group, which might have been stressful for their participating neonates (
The results of another study by Boo et al. (2002) indicated that preterm neonates’ exposure to twelve-hour cyclical lighting and continuous darkness was not effective in increasing their weight. Moreover, they found that their groups did not differ significantly from each other regarding the length of neonates’ hospital stay, the mean age at the time of regaining birth weight, the mean weight gain on the fourteenth day of their study, the mean weekly weight gain (24 gr), the mean daily weight gain, and the mean body weight at hospital discharge. They finally concluded that neither twelve-hour cyclical lighting nor continuous darkness had significant effect on weight gain among neonates (
3). The difference between our findings and findings reported by Boo et al. (2002) may be due to differences in the intensity of NICU lighting, the type and the length of the interventions, and the type of care services provided for neonates. Besides, Boo et al. (2002) conducted their study on neonates, who received mechanical ventilation, while our sample included no mechanically ventilated neonates.
According to Mirmiran et al. (2003), hospitalized neonates experience great stress induced by stressors such as constant and chronic exposure to poor or strong lighting, maternal separation, deprivation from maternal cuddle and deep sleep, and reactivity to light and sounds. Therefore, they conducted a study in 2003 in order to test the following hypothesis, “Neonates’ sleep pattern and circadian rhythm are developed independently from environmental lighting”. Consequently, they allocated nineteen neonates to a continuous darkness intervention and 21 to a cyclical lighting intervention. One of their findings was that sleep pattern development was positively correlated with neonates’ age (
2). Besides, they found that between-group mean differences of neonates’ body weight at the age of 35 weeks (106 gr) and four months (181 gr) were not statistically significant, respectively ( 2). Although the length of their study was longer than ours, their findings showed the ineffectiveness of lighting procedures on neonates’ weight gain. This is contrary to our findings probably due to the differences in neonates’ gestational age and lighting intensity in these studies. In our control group, the neonates were treated with continuous lighting while Mirmiran et al. (2003) treated neonates in their control group with continuous darkness. Seemingly, continuous darkness is less stressful for neonates than continuous lighting, resulting in insignificant difference between the groups in the study of Mirmiran et al. (2003).
Brandon et al. (2002) compared the effects of cyclical lighting and continuous near darkness on the growth of preterm neonates born at a gestational age of less than 31 weeks. They allocated the neonates in the cyclical lighting group to three subgroups as follows: 1. cyclical lighting since birth; 2. cyclical lighting since the 32nd post-conception week; and 3. cyclical lighting since the 36th post-conception week. The neonates in the second subgroup showed better recovery compared to the other two subgroups. They concluded that compared with continuous darkness, cyclical lighting is more effective in promoting weight gain. In other words, continuous darkness has no merit over cyclical lighting. The findings reported by Brandon et al. (2002) showed that their intervention was more effective than ours in increasing weight gain. This difference is probably due to the fact that their intervention was implemented for a longer period of time (six weeks) and with a different method compared to ours (
In another study, Mann et al. (1986) investigated the effect of cyclical day and night lighting and continuous lighting on neonates’ weight gain pattern, and reported a significant difference between these two lighting interventions. It is important to mention that this difference was observed only after hospital discharge. In the cyclical lighting group, the means of neonates’ weight at weeks six and twelve were significantly higher than the continuous lighting group. Besides, post-discharge weight of the neonates in the cyclical lighting group was by 0.5 Kg greater than the neonates in the continuous lighting group (
14). The study by Mann et al. (1986) was similar to the present study in terms of the type of interventions and the length of each 24-hour lighting course. Nevertheless, neonates’ weight gain in their study was greater than ours. Probable explanations for these differences may be differences in neonates’ gestational age, baseline age, the length of interventions, and the amount of silence at NICUs. Rivkees et al. (2004) also found that cyclical lighting synchronized with normal day and night was more effective than continuous dim lighting in increasing weight gain since the sixth week of their interventions. They found that in the continuous lighting group, the means of neonates’ weight at birth and at hospital discharge were 1110 and 2338 gr, while these values in the cyclical lighting group were 1072 and 2252 gr, respectively ( 9). In fact, the results reported by Rivkees et al. (2004) illustrated that day-night synchronized cyclical lighting does not significantly affect neonates’ weight gain during the first days of the intervention. The pattern of weight gain in our cyclical lighting group compared with continuous lighting group was slightly better than that reported by Rivkees et al. (2004). This slight difference can be attributed to differences between the studies regarding the neonates’ gestational age, neonates’ baseline age, the length of the interventions, and the type of care services provided for the neonates.
In line with our findings, the results of a study done by Miller et al. (1995) also indicated that compared with continuous lighting, cyclical lighting was more effective in increasing weight gain among preterm neonates. They reported that the mean of weight gain in the cyclical lighting group was significantly greater than the continuous lighting group (9.4% vs. 7.4) (
Some of the previous studies reported the ineffectiveness of cyclical lighting in promoting weight gain among preterm neonates. Discrepancies among the studies can be attributed to different factors such as the design and the length of studies. The important point here is that cyclical lighting can be beneficial for the development of neonates’ circadian rhythm. Consequently, it is better to place preterm neonates in appropriately-lit environments in order to promote their growth and development.
The pattern of weight gain in the experimental group was better than the control group. However, this study cannot provide conclusive evidence concerning the effect of different lighting techniques on neonates, particularly preterm infants. Alternately, the present study can be considered as a basis for more comprehensive studies. Further studies on the effects of cyclical lighting on preterm neonates can help promote their health.