Light is an important aspect of an animal’s environment and key component in the poultry production as it controls physiological and behavioral processes in the bird. Light helps the bird to establish rhythmicity and synchronize many essential functions, including body temperature and various metabolic steps that enhance feeding and digestion. There are three major functions of light on birds i.e to facilitate sight, to stimulate internal cycles due to day-length changes, and to initiate hormone release.  Avian species as well as mammalian species respond to light energy in a variety of ways, including growth, reproductive and productive performance.  Appropriate lightening allows adequate flock inspection, facilitates access to feed & water, minimizes injurious behavior, supports optimal production, provides rest period for birds and supports normal eye development in the poultry.

 Since the beginning of intensive poultry production light has been an important management tool to regulate poultry production, health and welfare. Actually, nutrient concentration, feed form and light act independently and also interactively. Light also stimulates secretory patterns of hormones that have a role in growth, maturation, and reproduction. Especially, light has an impact on the pineal gland and helps in synchronization of circadian rhythm and inhibiting melatonin release. The circadian rhythm helps the bird to optimize their metabolism, physiology and behavioral pattern.

At the present situation, a number of lighting program (wavelength, intensity, and duration) and devices are utilized by the poultry producers. The emphasis of poultry lighting has been placed on various light colors (e.g., blue, green, red, and white) and lighting sources (e.g., incandescent, fluorescent, and LED lights) in more recent decades.

Research has demonstrated that red lights have an accelerating effect on sexual development and maturity of poultry. In contrast, blue lights were found to be more associated with improving growth, calming the birds, and enhancing the immune response, although the underlying mechanisms have not been clearly delineated.

Avian vision

Chickens possess normal vertebrate trichromatic vision and can readily be trained to discriminate colors. They differ from mammals in that light penetrates the skull to influence the hypothalamus and in particular reproduction. Because photoperiod, which is essentially a change in light intensity, is known to influence the growth and behavior of meat chickens.

The chicken (Gallus gallus) possesses seven photoreceptor cell types including one rod and six cones. They have tetrachromatic color vision mediated by four types of single cone which are maximally responsive to violet, blue, green and red light. Double cones, in contrast, consist of pairs of closely apposed principal and accessory members which act as a single functional unit and are thought to mediate luminance detection that is used for motion perception.

Characteristics of Light

Management of light has emerged as one of the crucial managemental tools for poultry production. The influence of light results from a combination of light sources, light intensity, light color, and the photoperiod regimen. At the present situation, a number of lighting program (wavelength, intensity, and duration) and devices are utilized by the poultry producers. The light characteristics that effect on the chicken biology is the light duration, light intensity, and light colour. So, looking to these characteristics, light can be classified according to its four properties affecting growth, production, reproduction and welfare.

  1. Sources of light
  2. Its intensity in terms of illumination.
  3. Colour
  4. Duration of light

1.Sources of light- The main source of light on Earth is the Sun i.e. Natural source. Historically, another important source of light for humans has been fire, from ancient campfires to modern LPG  With the development of electric lights and power systems, electric lighting has effectively replaced firelight and are called Artificial light providing sources.

2.Intensity in terms of illumination- Illumination on a surface is measured in foot-candles. A foot candle is defined as the intensity of light striking each and every point on a segment of the inside surface of an imaginary one-foot radius sphere with a one candlepower source at the center.  Thus one foot candle equals one lumen per square foot. 1 foot candle = 1 lumen=10.76 lux.

Light intensity has a strong impact on broiler behavior. In general, brighter light will result in increased activity, while decreased intensities are effective in controlling aggressive acts that can cause cannibalism. Modern electronic systems are commonly used by the producers to increase light intensity for short periods during grow-out to increase exercise and thereby reduce skeletal and metabolic disorders. In the case of broiler, during the early part of life (brooding age) a minimum light intensity of 20lx is used. Following the early period, the restriction of both light intensity and duration is a common practice. Continuously low light intensities (1 lux or less) can have negative impacts on poultry welfare, and have been associated with increased foot pad lesions and poor eye development in meat chickens. Light intensity should be sufficient to allow young birds to find feed and water in the first days after placement in housing. Recommended light intensity for the first 3-7 days (20-50 lux) is generally higher than for the rearing / growing period for the commercial flocks (5-10 lux).

3. Colour

The use of LEDs can be an important way of lowering production costs since poultry farming is a long-term production activity.  Colour of light did not affect hen-day egg production, mortality or egg weight in layer farms. There are two mechanisms of muscle growth: hyperplasia (increase in fiber number) and hypertrophy (increase in fiber size). The process of muscle fiber development is nearly complete at the time of hatch. Post-hatch muscle fiber growth occurs through muscle fiber enlargement or hypertrophy, which results from the recruitment of satellite cell nuclei. As satellite cells are the only source of additional nuclei in skeletal muscles of chickens, various studies suggested that the higher muscle weight found in the green and blue light groups may be due to increased satellite cell proliferation during the first days of age. Birds reared in red or white light were more active, as expressed by greater walking activity in the white light treatment and by greater floor-pecking, wing-stretching, and aggression in the red-light treatment. As far as FCR is concern maximum FCR recorded in green light followed by yellow light and red light. Immune function of poultry is affected by light color and blue light has been shown to enhance the immune response. These results might have been due to the calming effect of the blue treatment on chicken activity. Moreover, blue light would alleviate the negative effects induced by the stress response, subsequently leading to a well-balanced immune response status. Hence, blue light may play a vital role in alleviating the stress response and improve the immune level in poultry. Light color can affect the immune performance of chickens in the early part of the rearing period and may subsequently influence the mortality of layers during the laying period. In addition, the photoreceptors in the hypothalamus of the poultry are more sensitive to blue and green light than red light.

4. Duration of light

During the brooding period, lightening duration is generally maximized to allow chicks to access feeding and watering equipments. Continuous lightening is not recommended, but may be left on for 23 hours a day in the first 3-7 days. Alternatively, intermittent lightening (4 hrs on, 2 hrs off) may be used for layers chicks during the first week after placement. One hour darkness is provided to accustom to avoid panic in the event of black-out. After brooding period, light period is adjusted to maximize the pullet growth and optimize the sexual maturity. There is a slow step-down of lightening from 0-8 weeks, until lights are on for 10 hours of the day. After which there are gradual increases in light from 16-30 weeks of age. A slower step-down of light hours from 0-12 weeks can be used to prevent early sexual maturity, maximize pullet growth and promotes early egg size.

Lighting duration that is photoperiod is the second major aspect of light that alters broiler performance. Most analysis involving light-weight management has targeted on this issue. The study showed better broiler performance at continuous lighting. Continuous light or 23L:1D is generally used in commercial production, which allows for maximum growth rate. Lighting length is generally dependent upon the age of chickens concerned and sort of housing in use. Research and discussion continue in an attempt to define the optimal photoperiodic regime suitable for chickens. However, broilers need to be provided 4 hr for sleep, but they, may require higher hours at certain points of growing period.

Arrangement Of Light Source

The arrangement of light in poultry house is very important for effective management and sustainable production potential. The lamps should be placed at adequate area so that the maximum illumination value is spread over the largest area. This all depends upon the physical dimensions and equipment in your building. 1 Watt light intensity per 1 to 1.5 birds or per 0.28 m2. 40-Watt bulb for 9.3m2 floor space.  Bulb height: 2m above the floor and distance between two bulbs should be 2.5m to 3m. Lower lamp is 1.8-2.0 m away from the ground and the upper lamp is 0.2-0.4m away from the top of the chicken coop. The distance between bulbs should be 1½ times the distance from the bulb to the bird level. The distance from the bulbs to the outer edges of the house should be only ½ the distance between bulbs. In cage system, the bulbs should be placed in such a way that their rays fall on the feed and on the birds. Clean reflectors increase the light intensity at bird level by 50%, compared with no reflector. Avoid cone shape reflectors since they confine the light rays to limited area.  Better to use flat type reflector with rounded edge. In case of deep litter system, the bulb is to be placed at 7-8’ height whereas in cage house, keep in aisle. Avoid hanging bulbs by a cord in open houses.