The production of eggs is associated with the length and intensity of light that the bird receives daily. Light stimulates the anterior lobe of the pituitary gland for the release of FSH and LH through the optic nerve. The role of Light in egg production is fully discussed here.
The light energy penetrates the skull, skin, and feathers, too. FSH is boosting ovarian follicle growth. Upon maturity, the ovum is released through LH’s action.
Significant points about light
- Wavelength from 400 to 700 microns (nanometer) which is visible to the eye
- The longer visible light wavelengths (red) are more able to reach the brain than the shorter wavelengths.
- The intensity of the light rays in the sun varied because of
- The position of the sun
- The cloudiness of the weather
- The dust and moisture present in the air
- Daylight duration varies because of the relative position of the earth to the sun
- North Hemisphere,
- 21st June is the longest day of the year
- 21st December is the shortest day of the year
- It is reversed in the southern hemisphere
Daylight occurs from 15 to 30 minutes before sunrise and darkness occurs 15 to 30 minutes after sunset due to the curvature of the earth’s crust and therefore the length of daylight is much greater than the hours between sunrise and sunset. But sunrise-sunset time is usually considered as the light day.
Words used with respect to light
A candela is the luminous intensity unit of a light source in a given direction
The lumen is characterized as the rate at which light falls on a square foot surface that is just as far away as one foot from a source with one candela in intensity.
In foot-candles, the illumination on a surface is measured. A foot-candle is defined as the intensity of light that strikes any point on a section of the inner surface of an imaginary one-foot radius sphere with a single candle-power source in the middle. One footcandle therefore equals one lumen per square foot.
A lux intensity of light equals one lumen per square foot.
1 Foot Light is equal to 10.76 lux
Types of light
There are four common types of light used in poultry houses,
Incandescent least expensive; requires reflectors, short bulb life (750-1000 hrs.)
Fluorescent-3 to 4 times more efficient than light bulbs; 10 times longer life than light bulbs
Mercury vapor-Long life (24,000 hrs.); it takes several minutes to warm up; it cannot be used in low ceiling houses.
Compact fluorescent (CF) lighting-More efficient energy. One-fifth fluorescent light energy is needed to provide the same intensity of light (lumen)
- The way lights are installed in the poultry house has a role to play in their performance. Some of the key points about the fixation of bulbs in poultry houses are,
- The gap between the bulbs should be 11⁄2 times that from the bulb to the level of the eye.
- The distance between the bulbs and the outside edges of the house should be just 1⁄2 the distance between the bulbs.
- The bulbs should be placed in cage systems in such a way that their rays fall on the feed and the birds.
- Clean reflectors increase light intensity by 50 percent at bird level compared to no reflectors.
- Avoid reflectors of the cone shape since they confined the light rays to a limited area. Better to use rounded-edge flat-type reflector.
- In the case of a deep litter system, the bulb should be placed at a height of 7-8′ whereas, in a cage house, it should be kept in the aisle.
- Stop hanging the bulbs in open houses by a string
- Very dirty bulbs emit less than 1/3 of light than clean bulbs.
- Cleaning the light bulbs once in two weeks.
Effects of light during the growing period
Reducing the length of light day during growing periods would result in
- Increase age when sexually mature
- Increase the number of eggs laid during egg development in the first half (but not in the total number of eggs laid)
- Grow the size of the first produced eggs.
Light restriction alone delays sexual maturity by up to 3 weeks at most. If feed restriction is combined with light restriction we may delay a period of up to 4 weeks.
Effects of light during the laying period
Birds reared under increased daylight develop more eggs because the pituitary releases FSH and LH. Light shine also affects the development of eggs.
In layer houses, the intensity of 1 ft. of candlelight is necessary under realistic conditions. At the lower deck, a minimum of 0.5 feet of candlelight intensity is needed in the multi-duck cage system. 16 hours of light during peak egg production period is required for maximum egg production.
Reducing the photoperiod during laying time seriously affects the development of eggs. The artificial light can be provided in the morning, in the evening or morning, and in the evening.
Combination of both growing and laying lighting programs
Two important points about lighting to remember are,
- For growing pullets, the length of the light day should never increase.
- For the laying of pullets, the length of the light day should never decrease.
Flocks at season
Those birds which are grown during a time when the duration of the natural light day is decreasing, are called in-season flocks at least during the last part of their growth cycle. As a general rule, chicks hatched in the Northern Hemisphere between 1 March and 31 August are called in-season flocks.
Flocking out of season
Chicks hatched between the 1st of September and the 28th of February are called out-season flocks, as their growing period falls on the daylight.
Instructions for light programs in open-sided buildings
A) Flocking in season
There is no need for artificial light up to 20 weeks (22 weeks for meat-type breeders). At age 20 weeks, the light is increased to 13 hours. Then add 1 hr. a week before light hits 16 hours.
B) Flocking out of season
There are two ways to adopt
Light-day program permanent
Determine the length of the longest day of natural light until the pullets hit 20 weeks of age. Maintain this average light hour span from the 3rd day until 20 weeks by supplementing natural light with artificial light. Then, at this point, increase 1 hour of light and increase 1 hour per week until the total light duration reaches 16 hours.
Daylight Diminishing program
Determine the total natural hours of daylight when the pullets reach 20 weeks of age. Then, add seven hours. This represents the length of daylight from day 3. The length of the light day is then shortened by 20 minutes per week. At age 20 weeks the length of the light day increases by 1 hour. Then growing for 1 hour per week until it reaches a light of 16 hours a day.
Photo-refractoriness is a condition in which the bird cannot respond to the lengths of the long day. The longer the stimulating day, the sooner and the more pronounced the photo-refractory reduction in egg production.
Ahemeral light programs
If the total light and dark period is not twenty-four hours, we can call it the ancient lighting cycle. Two types exist: Longer day (14 hr. light + 14 hr. dark) and shorter day (11 hr. light + 11 hr. dark).
The longer day cycle increases the quality of the eggshell, since the shorter day cycle increases the production of eggs by 2%. These cycles, however, are not compatible with the normal schedule of work and need light-proof houses.