Poultry vision system
Chickens perceive light through their eyes and their skull (pineal gland and hypothalamus). The retina’s rods and cones detect light, with cones discerning colors and brighter light, and rods perceiving objects in low light. This advanced visual system allows chickens to respond to a broader color spectrum and they have higher visual sensitivity than humans. Unlike humans, who respond to light wavelengths ranging from 400 to 750 nm, chickens can also see UV light (315–400 nm). Chickens exhibit increased sensitivity to red and blue light, with notable sensitivity peaks at approximately 480 nm and 630 nm. This broader and more intense spectral sensitivity means that poultry respond differently to light than humans, necessitating specialized lighting conditions to optimize their growth and productivity. Additionally, light penetrating the skull can affect extra-retinal photoreceptors.
The pineal gland regulates serotonin and melatonin, influencing circadian rhythms (a 24-hour cycle) and their hormonal and behavioral patterns. The hypothalamus modulates gonadotropin-releasing hormone (GnRH), affecting the pituitary and gonads, thus influencing growth and physiological activities. Designing a lighting environment tailored to poultry vision can enhance social interactions, location, and feed and water utilization, ultimately improving bird welfare and production efficiency.
Effects of light parameters on poultry
Light intensity and its measures in humans and poultry
Proper light intensity (brightness) ensures chicks adapt to their environment, optimizing feed and water intake, and minimizing stress. The measurement of light intensity involves different standards for humans and chickens. Lux is based on the human eye’s peak response at a wavelength of 550–560 nm, as per the International Commission on Illumination (CIE) standards. In contrast, chickens have three photopic spectral peaks, requiring additional calculations to measure light intensity accurately for them, termed clux. Depending on the light source and its peak spectrum, clux values can be up to 50% or more intense than lux values.
Understanding the distinction between lux and clux is crucial for poultry producers. It enables more accurate selection of light bulbs tailored to the specific needs of chickens and highlights the limitations of traditional light meters. While a traditional light meter can provide a general indication of light intensity, it does not account for the differences between lux and clux, leading to potential discrepancies. Thus, a clux meter is essential for precisely measuring light intensity tailored to poultry vision. Discover more about the clux meter in our Tool of the Month article. The following Table shows lighting intensities in clux and their lux equivalent (adopted from Olanrewaju et al., 2019).
| CLUX intensity (for chickens’ vision) | LUX equivalent (for human vision) |
| 25 | 17.4 |
| 10 | 7 |
| 5 | 3.5 |
Light source
Traditionally, incandescent (ICD) bulbs were common in poultry farms but have been phased out due to high energy consumption. Alternatives like cold cathode fluorescent lamps (CCFL), compact fluorescent lamps (CFL), and light-emitting diodes (LED) offer energy efficiency, long life, and varying wavelengths.
LED lighting has revolutionized poultry barn lighting by offering full-spectrum light that aligns with poultry’s broader perception range, including ultraviolet (UV) wavelengths. Studies have shown that transitioning from outdated incandescent light bulbs to LED provides better energy efficiency and the ability to control the light spectrum. LED lights, particularly monochromatic ones, are emerging as the best option for broiler production, improving hatchability, chick quality, and immune function while reducing stress susceptibility. LED lights, especially yellow LEDs, have shown superior performance in body weight gain and manure reduction.
A key challenge with LED lighting has been its reliance on a human-based vision scale for light intensity, which may not reflect the actual intensity as perceived by poultry. This reliance can impact physiological welfare indices, potentially affecting bird behavior and welfare. As previously noted, researchers have introduced the concept of clux, a measure of light intensity tailored to the spectral sensitivity of poultry, to overcome this limitation. Clux offers a more accurate representation of light intensity for poultry, leading to better physiological welfare and reduced stress.
Olanrewaju et al. (2019) investigated the effects of two types of LED light sources (red-supplemented vs. unsupplemented) on male broiler chickens. The lights were adjusted to either human spectral sensitivity (measured in lux) or poultry spectral sensitivity (measured in clux). This study evaluated the impact of these lighting variations on selected blood physiological variables. Looking at the physiological variables of the birds, the study concluded that adjusting light intensity to poultry-specific spectral sensitivity (clux) does not negatively impact broiler health and welfare. This emphasizes the importance of designing lighting systems based on clux measurements to ensure they meet the specific needs of poultry, thereby promoting optimal health and production. These findings support the notion that lighting decisions should be driven by economic considerations without compromising bird welfare.
Flickering
Light flicker, which refers to fluctuations in the brightness of a light source, can affect the behavior and stress levels of poultry. While light flicker might not be noticeable to the human eye at higher frequencies, poultry can detect flicker at much higher rates. For instance, passerine birds can perceive light flickering at up to 145 Hz, and electroretinogram (ERG) studies suggest that laying hens can detect flicker at frequencies exceeding 100 Hz. Even if chickens can’t consciously perceive flicker above 87 Hz, they might experience stress and other adverse effects from high-frequency flickering that go unnoticed by humans.
Raabe et al. (2024) studied the effects of flickering LED lights on male fattening turkeys. Unlike traditional incandescent bulbs, LEDs require specific power circuits, and the fluctuations in current can lead to light flicker. Their findings showed that flicker frequencies of 165 Hz, 500 Hz, and 16 kHz did not lead to significant differences in live weight development and feed consumption. These flicker frequencies did not influence the rates of injurious pecking. Additionally, they had no impact on feather corticosterone concentrations, which indicate stress. Based on these findings, the researchers concluded that flicker frequencies of 165 Hz or higher do not adversely affect turkey growth, feeding behavior, or stress levels.
Light color (wavelength)
Chickens can perceive light in the 315-750 nm range, with sensitivity peaking at 562 nm. Light color impacts development, with short wavelengths (blue, green) stimulating early growth and long wavelengths (orange, red) accelerating maturity. Monochromatic green light during embryogenesis and early post-hatch enhances growth and immunity. Blue light improves resistance to heat stress and modifies activity levels, contributing to welfare. Combining different light colors, like green and blue, can synergistically enhance growth and immune function. The following Table summarizes different monochromic light colors (wavelength) on chickens’ performance and welfare (adopted from Wu et al., 2022).
| Light color | Performance or welfare measures |
| Ultraviolet ray | Increase in: Body weight gainReduction in:MortalityWing flappingStress indicators (plasma corticosterone and heterophil: lymphocyte ratio) |
| Purple light | Reduction in:Body weight gainMeat quality |
| Blue light | Increase in:Body weight gainFeed efficiencyGizzard and gut weightBreast muscle weightMelatonin hormoneReduction in:Hydrocarbons from litterHeat stress effectsCorticosterone hormone (stress) |
| Green light | Increase in:Body weight gainT lymphocytes proliferation (immunity)Walking abilityEating and drinkingPreening and body shakingReduction in:Adrenocorticotropic hormone (stress)AggressionFeather pecking |
| Yellow light | Increase in:Meat qualityReduction in:Walking Eating |
| Orange light | Reduction in:Movement and droppings |
| Red light | Increase in:WalkingHead movementWing flappingReduction in:Eating and drinkingFlyingSittingMelatonin hormoneInsulin-Like Growth Factor-1 (IGF-1) |
| Far infrared ray | Increase in:Body weight gain Feed efficiencyReduction in:Ammonia emission hydrocarbons from litter |
Understanding and implementing an optimal lighting regimen is essential for maximizing the growth, health, and welfare of broiler chickens. Different light spectra and intensities significantly impact various physiological and behavioral outcomes. By tailoring lighting conditions to meet the specific needs of the flock, poultry producers can improve body weight, feed efficiency, and meat quality while minimizing stress, mortality, and aggressive behaviors. Applying these insights to poultry management practices can result in more efficient production, healthier birds, and ultimately, greater economic benefits.
References
Hy-Line International Technical Services Team. 2017. Understanding poultry lighting. Zootecnica International (link)
Olanrewaju, H. A., J. L. Purswell, S. D. Collier, and S. L. Branton. 2019. Effect of light intensity adjusted for species-specific spectral sensitivity on blood physiological variables of male broiler chickens. Poultry Science 98:1090–1095 (link)
Raabe, J., G. Raveendran, W. Otten, K. Homeyer, and T. Bartels. 2024. Research Note: Irritating flashing light or poultry-friendly lighting—are flicker frequencies of LED luminaires a potential stress factor in the husbandry of male fattening turkeys? PoultryScience103:103214 (link)
Wu, Y., J. Huang, Sh. Quan, and Y. Yang. 2022. Light regimen on health and growth of broilers: an update review. Poultry Science 101:101545 (link)
Mohammad was the PIP team Research Associate (2021-2024) with extensive experience in poultry nutrition. He wrote science articles for newsletters and worked on developing adaptations and recommendations to support the adoption of new managerial tools, products, services, and practices by the poultry industry.
Looking at his poultry industry perspective, Mohammad has been serving the poultry industry through his extensive experience in feed formulation as an animal nutritionist over the past ten years. He was also a university lecturer for 10 years. Mohammad was a member of the Animal Care and Use Committee (ACUC) at the U of A. Mohammad graduated with a Ph.D. degree in Animal Science from the University of Alberta with a Postdoctoral fellowship before moving to his Research Associate position with the PIP team. Serving the poultry industry as an animal nutritionist for more than a decade, Mohammad loves teaching and worked as a university lecturer in Iran and a teaching assistant at the U of A. Mohammad was inspired by Dr. Frank Robinson, practicing the inquiry-based learning method when working as a TA in his “Principles of Animal Agriculture” class. “I have a strong passion on poultry nutrition and have always loved to help poultry producers with optimizing the poultry systems. The challenging part of working with live animals is that you need to be on call even as a nutritionist. However, the joy of seeing healthy animals and help with their welfare overcome the challenging part.”
