Abstract
Light serves as a critical environmental modulator, influencing productivity, physiology, and welfare of layer birds. It plays an important role in biological signals in harmonizing circadian rhythms, modulating endocrine activity, and controlling critical reproductive events. Advances in light technology, such as new programmable light-emitting diode (LED) systems, UVB –LEDs, and dichromatic incubation light, provide chickens with specific light colors and intensities for hours each day. These advancements offer greater opportunities to optimize egg production efficiency and improve chicken welfare than previously adopted lighting techniques. In this present mini-review, current knowledge of the effects of different lighting programs, such as step-up, step-down, intermittent, and constant regimes, on feed intake, reproductive hormone response, laying rate, egg quality, and longevity in commercial layers is discussed. Studies show that moderate photoperiods (14–17 h/day) optimize follicular development and laying performance. This is achieved by influencing melatonin rhythms that regulate reproductive hormones. In contrast, continuous light suppresses melatonin and disrupts follicle maturation and calcium metabolism, leading to poor shell quality and accelerated reproductive aging. Also, pulsed compact-lighting programs improve body weight, eggshell strength, and feed efficiency by allowing physiological recovery during dark hours. Furthermore, red-, blue-, and green-light using LEDs facilitate wavelength-specific modulation of stress, metabolism, and reproductive hormone activity. Different studies have shown that green light during the first 18 days improves chick weight by 37%, body weight gain, and weight gain. Furthermore, the productivity and welfare of layers are influenced by different wavelengths, exposure duration, light spectrum, and distribution patterns. Therefore, further research is needed to develop strain- and climate-specific lighting programs and to consider smart LED systems with circadian-responsive controls for sustainable, welfare-based egg production in modern poultry facilities.

Key words: Photoperiods; egg production; avian physiology; productive traits; reproductive hormones