# Research Progress and Effects of Light on Poultry Circadian Rhythm Regulation Based on CiteSpace
## 3 Effect of Light on Poutlry  
As shown in Sections 2-4, light is one of the most important environmental factors for poultry. Light intensity, wavelength, photoperiod, and spectral composition have certain effects on poultry welfare, yield, and growth and development, especially for chickens [19]. In recent years, light sources with low cost and long life (such as LED lamps) have been paid attention to and widely applied in the poultry industry. Different light sources with different light intensities and wavelengths provide a new alternative strategy for improving poultry welfare, production performance and commercial returns to choose the right light source. Light also affects the growth and development of poultry. In the early stage of growth, chicks raised under green light grow faster than the others [20,21]; however, chicks raised under red light grow slowly [22]. During the incubation period, green light, red light, blue light, and white light all suggested a promoting effect on the growth and development of embryos [23,24]. Appropriate photoperiod can also promote poultry growth and weight gain [19]. Broilers exposed to flickering light and intermittent feeding had the highest body  
Figure 5: Timeline view of research frontiers (The size of the node is proportional to the number of citations of corresponding documents. Purple color outer circle represents high centrality, and red color outer circle represents high citation of important documents). weight. In addition, the study found that broilers exposed to flickering light had higher quality than broilers exposed to continuous light. In addition, studies on the relationship between light and productivity provide a new way to improve the productivity of poultry. Long-wavelength light was more effective in promoting poultry reproduction than short-wavelength light. Long-wavelength red light can lead to stronger ovarian activity [25], promote sexual organ development in chickens, enhance sex hormone secretion and sexual maturity of chickens, increase the laying rate [26], and increase the fecundity of pigeons [27]. It can also improve the sperm quality of cocks and the egg production of laying hens and quails. Except for wavelength, photoperiod also has certain effects on the reproductive performance of livestock, supplementary artificial light can increase the reproductive capacity of geese [28], and exposure to 12 h of darkness reduces the spawning of birds [29]. In addition, uneven light affects the production performance of chickens [30,31]. In addition to animal welfare, light has a certain effect on the immune function of poultry. As for the immune function, the immune function of embryos cultured under red and blue light was stronger after hatching compared with that of embryos cultured under white light [32,33]. In addition to the influence of different light sources, photoperiod is a factor affecting the immune function of poultry. [PERSON] et al. found that intermittent light considerably improved the nonspecific immunity of broilers compared with continuous illumination for 24 h [34]. [PERSON] et al. also thought that the immune function of Peking ducks exposed to 20 L:4D photoperiod was higher than that of Peking ducks exposed to 16 L:8D photoperiod [35]. Light also has a certain effect on the hatching rate of poultry eggs and the welfare of poultry, such as stress response, comfortable behavior, fear, and depression. Light during incubation can reduce posthatching fear [36, 37, 38], and cubs hatched in light may cope better with posthatching stress conditions than those hatched in the dark, thereby helping them adapt well to the postnatal environment and improve their welfare [24,39]. However, exposure to different light sources during incubation produces different effects on the fear and behavior of poultry after birth; however, no unified conclusion has been achieved. Compared with green light, red light and white light are the key spectra to reduce fear and stress sensitivity in broilers [40].