Written by: Dr. Jacquie Jacob, University of Kentucky
Light is an important but often overlooked part of an animal’s environment. Aside from allowing animals to see their environment, light affects growth, reproduction, and behavior.
UNDERSTANDING HOW LIGHT AFFECTS BIRDS
To devise an effective lighting plan for your poultry house, it’s important to understand how birds perceive and respond to light.
Light is part of the electromagnetic spectrum, which is made up of electromagnetic radiation of varying wavelengths. Parts of the electromagnetic spectrum include radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays. Visible light is electromagnetic radiation at wavelengths humans can see. We see visible light as colors, with each color determined by wavelength.
Three factors affect an animal’s response to light. These factors are wavelength, intensity, and duration. As mentioned, wavelength determines the color of light. The order of the colors of visible light from the shortest wavelength to the longest wavelength is violet, blue, green, yellow, orange, and red. Intensity is the brightness of the light. Duration is the number of hours of light an animal is exposed to in a day. Birds are sensitive to wavelengths outside the human visible light spectrum. While we may perceive two different light sources as the same, chickens are able to see wavelengths of light that we may not be able to see. As a result, the behavior of the chickens may be different under the two light sources.
Birds detect light in two ways—through the eyes (retinal receptors) and through photosensitive cells in the brain (extraretinal receptors). For the extraretinal receptors to detect light, the light must pass through the skin and skull of the bird. Long wavelengths (toward the red end of the spectrum) penetrate the skin and skull more efficiently than short wavelengths. Different wavelengths affect birds in different ways. Short wavelengths detected by the retinal receptors affect growth and behavior. In contrast, reproduction is linked to the extraretinal receptors and thus long wavelengths. Also, it has been reported that blue light has a calming effect on birds and that red light can reduce feather pecking and cannibalism. Blue-green light has been shown to stimulate growth, whereas orange-red light stimulates reproduction.
CHOICE OF LIGHT SOURCE
When devising a lighting plan for your poultry house, you should consider lamp type, number of lamps, and placement of lamps.
The most common type of lamp used in poultry houses is the incandescent bulb (shown in Figure 1). Incandescent bulbs produce light by passing an electrical current through a thin tungsten filament, causing the filament to heat and glow. (This glowing due to high temperature is referred to as incandescence, thus the name for the bulb.) The light produced covers the entire visible light spectrum. Much of the energy produced from the electrical current is converted to heat energy, making the incandescent bulb very energy inefficient.
Because of increasing energy costs, alternative light sources have become popular for use in poultry houses. The most common of these alternatives is the fluorescent lamp (shown in Figure 2). Fluorescent lamps produce light by passing an electrical current through a low-pressure vapor or gas contained within the bulb. The ultraviolet radiation given off is absorbed by a phosphor material that coats the inside of the lamp. The phosphor material then fluoresces, or emits electromagnetic radiation at wavelengths that can be seen as visible light. The wavelengths that are given off depend on the type of coating used. Fluorescent lamps cost more but have a longer life and use less electrical energy than incandescent bulbs. If you are considering using fluorescent bulbs, keep in mind the following important factors:
- Many fluorescent lamps are not dimmable, so the light in the poultry house cannot be dimmed if cannibalism becomes an issue.
- Fluorescent lamps do not work well, and sometimes do not work at all, in very cold weather.
- The type of fluorescent lamp is important. Hens need warm-white fluorescent lamps to receive the correct spectral output (more orange and red) to maintain production. Chicks benefit from cool-white lamps, which are concentrated in the blue-green wavelengths.
Several new Light Emitting Dioxide (LED) lights have become available lately. When they first came out, LED lights were expensive and in some cases did not hold up or perform well in the environmental conditions common in poultry houses. Current models of commercial grade LEDs have overcome some of these early problems. LED lights are dimmable and provide good lighting uniformity. Auburn University has a good publication on the use of LEDs for broiler house lighting.
All light intensity is measured in lumens of output. Footcandles are used in the United States measure the lumens at bird level which is lumens per square foot. In countries using metric measurements, they use lux (lumens per square meter) instead of footcandles. One footcandle is equal to about 10.76 lux.
You should choose the correct number and placement of lamps to produce even light intensity throughout your poultry house. When setting the light intensity it is important to know that fluorescent bulbs lose up to 20 percent of their original light output during their life. If you are using fluorescent lamps, consider this factor when determining light placement. Also, dirty lamps give off reduced light intensity, so you should clean all lamps on a regular basis.
Strong light intensity is generally not required and can, in fact, result in bird stress and increased incidences of feather pecking and cannibalism. The general requirement is 2 footcandles for brooding and half a footcandle thereafter.
DESIGNING A LIGHTING PROGRAM
Lighting programs refer to the number and distribution of hours of light per day. This is particularly important for laying hens which are influenced by the number of hours of light per day. Increasing day length, as naturally occurs in the spring, stimulates sexual maturity in chickens resulting in egg production in pullets and sperm production in cockerels. Decrease day length, as naturally occurs in the fall, decreases egg and sperm production. By manipulating the number of hours of light per day by supplementing with artificial light, it is possible to keep laying hens in production through the winter.
Lighting programs for meat birds are mainly aimed at stimulating and controlling feed intake.
FOR MORE INFORMATION
Lighting for Small-Scale Flocks, Robert Hawes, University of Maine
The science of poultry lighting: A bird’s eye view. Once Innovations