The red light demonstrated significantly higher (p < 0.05) feed intake in line with Prayitno et al. (1977) study, based on color effects compared with all permutations of monochromatic and mixed-color light by broilers, agrees that birds' feed intake activity was higher in red than other light colors, although differences in perceived intensity of the different lights may have affected this. Red light performed better at enhancing feed intake in this study, a finding that is consistent with other literature that proposes that red light enhances activity and possibly hunger or food-searching behavior (Gulizia and Downs, 2021). The red-light wavelength may be more stimulating to laying hens, as it stimulates the endocrine system, which then stimulates the hens’ feeding actions. Therefore, the higher the light intensity, the higher the hens' feed intake throughout the day. The treatment of 25 lux was most associated with higher feed intake relative to the other treatments. Higher light intensity treatments make hens more visible and consume more actively (Liu et al., 2018). Second highest feed intake was observed in warm white which is consistent with studies that have demonstrated the benefits of stable lighting environments for reducing stress and enhancing productivity in poultry (Olanrewaju et al., 2018; Blatchford et al., 2009). Warm white light's unique anti-flicker properties are especially noteworthy. Studies have demonstrated that anti-flicker lighting enhances poultry performance by lowering stress levels and enhancing feed conversion efficiency (McPhee, 2023; Schwean-Lardner et al., 2013).
The highest body weights were observed in layers exposed to warm white light at 25 lux intensity. The combined effect of this specific light color and higher intensity appears to optimize the growth conditions for the layers, leading to superior weight gain. The results of our findings are in line with previous studies that found enhanced growth and productivity in poultry under optimized lighting conditions (Baxter et al., 2014; Lewis and Morris, 2006). Previous research supports that tailored lighting systems can improve poultry growth performance (Olanrewaju et al., 2006; Rozenboim et al., 2004). Warm white light, characterized by its anti-flicker properties, potentially reduces stress and visual discomfort in chickens (HATO, 2019). In chickens, flickering lights have been shown to cause stress to their nervous system, impairing their growth and welfare (Kavtarashvili and Gladin, 2022; Evans et al., 2012). The provision of a constant light source of warm white light at an optimal intensity probably offers a more consistent environment, promoting higher feed intake and more balanced growth patterns. Layers exposed to red light at 25 lux intensity had the lowest recorded body weights. This combination proved to be the least effective for promoting weight gain. The reduced growth under red light may be attributed to lower feed intake or suboptimal physiological responses, aligning with research indicating that red light can sometimes reduce growth rates in birds (Franco et al., 2022).
The findings from this study showed that warm white anti flicker light demonstrated higher body weight gain compared to other lights, which have anti flickering properties. According to Kavtarashvili and Gladin (2022), laying hens experienced higher mortality due to aggression and cannibalism, higher final body weight (BW) and higher feed consumption when housed under lower flickering light compared to a higher flicker light. These findings are in line with our results where warm white anti flicker light demonstrated higher body weight gain compared to other lights, which have anti flickering properties (Raabe et al., 2024). In addition, our experiment's comparison findings align with those of Jean-Loup et al. (2017), who observed that the utilization of extremely low light intensities throughout the layer production cycle can lead to reduced body weights by modifying behavioral patterns and decreasing active time. Mohammed et al. (2016) asserted that employing moderate light intensity is preferable in order to prevent aberrant behavior. The study conducted by Kavtarashvili and Gladin, (2022) and Evans et al. (2012) demonstrates that the performance of warm white light is greatly influenced by its high light intensity. The absence of flicker in the light is particularly important for optimizing the physiological reactions of layers.
The findings of this study suggests that white, blue, green, and yellow lights had intermediate FCR values, with green lights generally resulting in better feed conversion than white, blue, and yellow lights, which are line to the findings of Yang et al. (2016) and Riaz et al. (2021), who found that white light could improve FCR due to the establishment of circadian rhythms and better welfare. Furthermore, the superior FCR efficacy of warm white light aligns with the hypothesis that its anti-flicker properties may alleviate stress factors in layers (Kavtarashvili and Gladin, 2022; Evans et al., 2012). Previous scientific studies provide sufficient evidence to support the assertion that stress can have a substantial influence on the metabolic processes of chickens, which is evident in the quality of the conversion of feed into body mass (El-Naggar et al., 2019; Wang et al., 2018). The use of red light, while first appearing to stimulate bird activity and improve feed intake, can actually have a negative impact on feed conversion efficiency (Gulizia and Downs, 2021). The causes for this phenomenon can be attributed to heightened levels of activity or stress, which may not necessarily result in fruitful advancement. The FCR data further demonstrates the necessity for an ideal light intensity. The efficiency of FCR becomes more diverse as the intensity increases, particularly under red and warm white light. This implies that both the hue and intensity of the light have an impact on the birds' ability to convert the feed effectively. This also corroborates the conclusions of El-Sabrout et al. (2022), who stated that the use of suitable lighting systems can enhance the efficiency of the metabolic process. The latest research has confirmed that layers have a preference for light colors at different levels of light intensity. This information will be useful for managing LED colors to satisfy the needs of young chickens. Additionally, it has been observed that layer color preference changes during different phases of development (Li et al., 2019).
The layers that were exposed to warm white light had the lowest mortality rate. This finding is consistent with earlier research that has emphasized the advantages of stable, anti-flicker lighting settings for the performance and survival of poultry (Chew et al., 2021). A higher mortality rate was observed in the presence of red light, which contradicts the findings of Svobodova et al. (2015). They reported that laying hens raised under red light had the lowest mortality rate of 12.65%, while hens raised under blue light had the highest mortality rate of 14.30%. This suggests that birds reared under red light may be less susceptible to stress. Light wavelength has been demonstrated to affect behavior and stress levels (Sultana et al., 2013). Birds exhibit increased periods of sedentary or stationary behavior at shorter wavelengths, whereas they display mobility in longer wavelengths. Birds subjected to red/yellow light during their upbringing exhibit a longer duration of tonic immobility, suggesting a higher level of anxiety compared to birds exposed to green and white light. This increased fear response may potentially decrease the feeding time of the birds (Huber-Eicher et al., 2013). The greater mortality observed in red light during this experiment may be attributed to this factor. The data on light intensity indicate that greater intensities are often correlated with a little rise in mortality. This pattern suggests that when certain intensities are not optimized or aligned with the birds' needs, they can cause physiological stress and potentially increase mortality rates (Kang et al., 2023; Raccoursier et al., 2019). The simultaneous influence of light color and intensity has varied outcomes, as certain combinations, such as red at 25 lux, have been linked to heightened mortality rates. The aforementioned variances highlight the crucial importance of establishing a properly balanced lighting system in poultry environments to achieve optimal health outcomes and minimize mortality rates (Chew et al., 2021).
The findings of this experiment demonstrated significantly (p < 0.05) higher egg production in warm white light. Only two studies have evaluated the effects of light flicker during the egg production phase. While Wichman and Groot (2021) did not evaluate performance, Kavtarashvili and Gladin, (2022) have suggested that flicker exposure during the hen phase may influence hen performance. According to HATO (2023), when examining the hen-housed laying percentage and the hen-day laying percentage, both metrics demonstrated higher results when using flicker-free lighting compared to using flickering lighting. These findings are in contradiction with Baxter et al. (2014) and Huber- Eicher et al. (2013), who stated that laying hens kept under red light not only started to lay eggs earlier but also had higher egg production than birds kept in white or green light. Similar results were observed by Prayitno et al. (1997), where birds exposed to blue and green light were more sedentary than compared to red light and egg production remained low. According to Renema et al. (2001), hens exposed to lighting intensities of 5, 50, or 500 lux had a greater overall egg production compared to those exposed to one lux (148.3, 150.2, 147.9, and 142.2 eggs per year, respectively). The authors proposed that chickens exposed to one lux had a notably reduced occurrence of egg sequence during peak egg production compared to the groups exposed to 50 lux or 500 lux (55.2 vs. 79.3 or 74.7 days). However, there were no notable variations in egg production or fertility among the laying hens exposed to light intensities ranging from 11.3 to 18.7 lux (Ma et al., 2013). Contrary to our findings of Hsu et al. (1990), it was shown that geese exposed to light intensities ranging from zero to 40 lux did not exhibit any notable variations in egg production among the different groups. Reduced production under red light might be due to lower visual stimulation or different behavioral responses, aligning with findings that red light can sometimes result in lower reproductive performance in poultry (Huber-Eicher et al., 2013; Rozenboim et al., 2004).
The results from this study clearly demonstrate that both light color and intensity significantly (p < 0.05) influence the egg quality characteristics in layers, with variations noted across different weeks of production. Notably, warm white light, particularly at higher intensities like 25 lux, consistently yielded eggs of superior quality in terms of weight, specific gravity, and eggshell thickness. These findings are supported by multiple studies that highlight the benefits of stable, anti-flicker lighting environments in enhancing poultry performance. For example, Baxter et al. (2014), Schwean-Lardner et al. (2013) and Blatchford et al. (2012) both observed improvements in overall poultry well-being under optimized lighting conditions, which directly translates to better egg quality. The consistent inferiority of eggs produced under red light, irrespective of the intensity, suggests that not all wavelengths of light are equally beneficial, which is aligned with the findings of Cao et al. (2008), who noted that red light could potentially stress layers, thus affecting their reproductive outcomes negatively. Moreover, the interaction between light color and intensity, particularly the superior results seen with warm white light at 25 lux, points to the potential for fine-tuning lighting programs in poultry operations to maximize output. Integrating findings from Huber-Eicher et al. (2013) and Lewis et al. (2000), who studied the physiological impacts of light on poultry, suggests that both visual and non-visual photoreceptor systems in birds respond distinctly to different light spectra and intensities, affecting their biological rhythms and hormonal balances.
The results demonstrates that the inferior performance of red light, particularly in producing the lowest NDV and IB antibody titers and less optimal hormonal levels, except for a relatively high cortisol, indicates a stress response rather than a beneficial physiological adaptation. This highlights the potential negative impact of certain wavelengths on layer well-being and productivity in line to Baxter et al. (2014) and Blatchford et al. (2012).
Moreover, the effect of light intensity is also notable, with 20 lux showing beneficial results, albeit less pronounced than 25 lux under warm white light. This finding showed the importance of not only the type of light but also the intensity at which it is administered, which aligns with prior research emphasizing the need for consistent and flicker-free lighting environments in poultry settings (Huber-Eicher et al., 2013; Schwean-Lardner et al., 2013; Rozenboim et al., 2004; Lewis et al., 2000). The overall data from our findings suggest that warm white light, particularly at higher intensities, significantly enhances the immunological and hormonal profiles of layers, potentially leading to improved overall health and productivity (Kavtarashvili and Gladin, 2022; Widowski and Duncanö 1996).
The results of the experiment showed that color of light, intensity of light and interaction of color and intensity of light significantly affect the cost of production of the birds at 30th weeks of age. Significantly lowest cost of production was observed in the birds kept under yellow light having 25 lux intensity and warm white light having 15 lux intensity respectively in line to Hassan et al. (2013). Due to the nonsignificant difference between above given treatments it can be calculated that any one of them may be used to reduce the cost of production at 30th weeks of age which are cosistant to findings of Olanrewaju et al. (2015), Wichman and Groot (2021), HATO (2023), Kavtarashvili and Gladinö (2022), whose findings demonstrated that optimized lighting not only enhances productivity but also reduces maintenance costs.