Light Stimulation of Commercial Layers

There is a dearth of scientific information about chicken vision, despite the fact that birds can see better than humans and are very sensitive to light. Recent study findings and practical experience support the idea that illumination regimens tailored to particular circumstances are an effective tool for managing laying hens. The key ideas are:

• Hens interpret the artificial light provided by incandescent lights operating in a frequency range of 50 Hz as flickering continuously. Hens love high frequency, or above 2000 Hz, incandescent or fluorescent lighting.

Commercial hens' vision is impaired by artificial light from standard light sources, whether filtered or unfiltered, which reduces the spectrum that is visible to them.

• Hens that have been raised in artificial light and then moved to natural daylight require some time to get used to the difference in how they see their environment. During the growth season, using "real light" lights that closely resemble the natural spectrum might lessen this impact.

• The basic idea behind stimulating hens in light-proof housing is to shorten the day before applying controlled light stimulation, then lengthen it afterwards. Egg production is negatively impacted by cutting down on light hours throughout the laying phase.

• Pullets should be raised in light-proof barns or in structures that can have their windows covered or uncovered in accordance with the lighting schedule.

• The so-called "darkening" of raising facilities to reduce the impact of fluctuating natural day length over a consistent time works well in open-air settings and should be considered as a possibility to enhance light stimulation in nations with hot climates.

• Light-proofing windows should be available in open homes for laying hens wherever feasible. The windows should be either entirely blacked out until the maximum day duration is achieved or covered and uncovered in accordance with the lighting scheme.

• Lighting schedules for pullets moved to open barns without the option of covering the windows in darkness should be adjusted to the flock's hatch date. The step-down during raising should be regulated such that the rise at transfer is no more than two or three hours in order to prevent a "light shock" when the days are particularly long.

• The length of the natural day, particularly in the spring and summer, has an impact on the growth of poultry raised in barns that cannot be light-proofed. Only by carefully altering lighting programs can premature commencement of lay be prevented, but light stimulation of such chickens is challenging, and their output often falls short of expectations.

Light and the Light Perception of Birds

Light is the visible part of the electromagnetic radiation. It plays an important role for the life of many organisms on earth. Light is perceived by them in different ways.

Most vertebrates use their eyes to sense light. When light enters the eye, it is focused onto the retina, a panel of cells that is sensitive to light. The retina's so-called cone and rod cells pick up light and transform it into the brain impulses needed for vision. The optic nerve subsequently carries the visual impulses to the brain, where they affect the birds' behavior and sex life. Additionally, the hypothalamus and pineal gland also contain some photoreceptors. The bird's life is also influenced by their stimulus. Birds have a different visual system than animals and people do. The already highly developed visual acuity of their reptile predecessors has been further improved in birds. They see the world differently and with far more clarity than we do. Birds are highly vision-dependent, avian species with morphological and physiological differences from humans due to their ability to fly and natural food sources. In particular, they include their tetrachromatic color vision and the capacity to differentiate extended visual sequences of up to 150–250 distinct pictures per second (humans can only perceive up to 25–30 unique images per second) (trichromatic in man). The latter is made feasible by the fact that birds' retinas have better photoreceptors than those of primates, allowing them to see colors in the spectral range between 360 and 400 and 600 and 700 nanometers. Birds have the ability to see in a UV spectrum that humans cannot see. When choosing artificial light sources and creating lighting schedules for pullets and laying hens, these aspects must be taken into account.

Sources of light and light quality
Incandescent lights, tubular fluorescent lamps, and more recently energy-saving lamps have all been employed as artificial lighting sources in pullet and laying house raising facilities. The use of modern, inexpensive LED (light emitting diode) technology is expected to increase in the next years, particularly if they are improved to generate a greater spectrum of light. In certain poultry businesses, high frequency light technology—also known as "true light" technology—that produces light that closely resembles the spectrum of the sun is already in use.

When the hens are four weeks old, the light intensity in light-proof pullet and layer housing is controlled for commercial reasons to around 5 Lux (raising) and approximately 10 to 15 Lux (producing) in order to minimize stress-related behavioral disorders.

The light source determines the light frequency. It is believed that poultry should not be exposed to fluorescent tubes or energy-saving lights that operate at low frequencies (50 Hz alternating current). Because of their keen eyesight, chickens can detect light flicker, which may negatively affect their behavior (nervousness, feather pecking and cannibalism). Therefore, it is preferable to use fluorescent tubes that operate at high frequencies (>2000 Hz) or incandescent bulbs whose flicker, despite the alternating current's 50 Hz frequency, is not noticeable due to their slowness. In most industrialized nations across the globe, incandescent lights will soon be outlawed because they are less effective than other kinds of lamps at converting electrical power to light.

The spectrum and frequency of the light output by the lamps have also been taken into account lately, although in the past the choice of light source was primarily based on economic concerns and the efficiency of the light source (light intensity). Systems that utilize filters to confine the light in poultry houses to certain colors (spectral ranges) are now being considered. It is thought that the blue, green, and red spectrums have various impacts on the chickens. Even yet, the majority of modern artificial light sources only cover a small percentage of the spectral range that is visible to birds. If there is sunlight, natural daylight has an intensity of more than 100.000 Lux and a frequency of up to 1015 Hz. It is evident that there is a significant difference in the quality of artificial and natural light, which may be experienced by the hens, depending on whether they are housed in barns with windows or walk freely in covered outdoor enclosures and range areas in the daytime.

Although the UV range (around 350 nm wavelength) seems to be significant for certain stimuli, such as those involved in the hunt for food and the behavior of birds during mating, conventional lamps do not cover this range.

In conclusion, conventional light sources create artificial light that is extremely inferior to natural light in poultry houses. Pullets that were raised in light-proof barns and then exposed to natural light thereafter view their environment differently and may experience stress as a consequence.

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