How Natural Light Works
Before we talk about artificial lighting and its affect on birds let’s briefly review the science of light.
The world around us is filled with electromagnetic waves (EM waves). In fact, there are hundreds, sometimes thousands, of EM waves moving through the room you’re in right now. Some of these waves are passing through you, while others are bouncing off of you.
The most important thing to know about EM waves is that
as their wavelength changes, their effect on living organisms also changes.
For example, you can see in the image below that the longest waves are radio waves and quite harmless. As the wavelengths get shorter, they become harmful radiation.
A Look at EM Waves Produced by the Sun (Sunlight)
Most EM waves are man-made; however, this article is about how artificial light compares to sunlight, so we will discuss EM waves that the sun produces. These EM waves have a wavelength between 100 and 1,200 nanometers.
The longest wavelengths that the sun produces are Infrared waves, otherwise referred to as heat.
The shortest wavelengths are UVC, which are 100% filtered out by the Earth’s atmosphere.
Ultraviolet waves between 280 and 400 nanometers are further broken down into categories A and B because the effects they have on living organisms are very different.
Wavelengths in the visible spectrum affect the color that we see
Within the visible spectrum, each wavelength is a different color. Light works by bouncing off of objects and into our eyes. When a light that contains wavelengths in the red spectrum bounces off of a red shirt, our eyes see red. If the light does not contain red wavelengths the shirtappears as a different color to our eye. That color depends on the wavelengths present in the light.
Therefore, a light with more wavelengths present is likely to make an object look more natural.
Mixing and Measuring Final Light
There are a limited number of colors in the visible light spectrum, but when they’re mixed, they produce different colors—much like mixing paint. Scientists estimate that the human eye can see over a million colors, which can be made by mixing various wavelengths of color. If a light were to contain an equal amount of every wavelength, the result would be white light. However, light rarely contains every wavelength, and it’s the mix of wavelengths present that determine the final color. Final color is measured by the Kelvin Scale (K).
When you purchase a light in the store, somewhere on the package will be the light color followed by the temperature in K. A regular household light, for example, is typically a yellowish light at about 3500K. The reason why light is measured in Kelvin rather than nanometers is because it represents the final color, not the individual wavelengths it contains.
The important thing to remember is that the K rating of a light is its final color and does not represent which wavelengths are present in the light to make the final color.
Optical Spectroscopes and Spectrographs
The color of light can be measured by an instrument called an optical spectroscope, which produces a report, called a spectrograph, as shown below. Sometimes a light will have a spectrograph on its packaging.
The written parameters of the report can be confusing, but if you look close you can see that this light is around 6,500K with a CRI of 94.
For the purpose of this article, the graph on the left contains more valuable information. It is a quick glimpse of which wavelengths (colors) are present in the light and at what intensity they are. As we learned above, in the graphic with the red shirt and blue shorts, the more wavelengths that are present, the more natural objects will appear to our eye.
For a fun reference, here is a spectrograph of the sun at noon on a cloudless day. The difference is pretty clear.
A bird’s eye can see more than a human’s
Birds have tetrachromatic vision, which means they can see the visible light spectrum plus the UVA spectrum. Bird experts believe this helps them with identifying food, species recognition, and mate selection. However, there’s no scientific proof that UVA has any effect on a bird’s health.
The other electromagnetic waves that have a direct impact on living organisms are in the UV spectrum
Scientists have subdivided the UV spectrum into many ranges but we will only be discussing the two that are relevant to bird lighting: UVA and UVB. Suntan and the creation of vitamin D are good examples of their impact.
UV wavelengths are invisible to the human eye and act differently than visible light. While they bounce off most objects, they sometimes penetrate them instead. For example, both UVA and UVB rays penetrate human skin. However, UVA rays penetrate deeper, all the way down to the hypodermis, while UVB rays only penetrate to the epidermis.
When UVA rays penetrate the skin, they produce melanin which causes skin to tan and wrinkle. UVB synthesizers produce vitamin D3 and, when absorbed in excess, can cause sunburn along with degenerative changes in cells, fibrous tissue, and blood vessels of the skin.
90–95% of UV radiation that reaches the Earth is UVA. It’s important to note that UVA is present equally throughout the daylight hours and seasons. It can also penetrate clouds and glass.
UVB makes up only 5–10% of solar radiation. It’s strongest between 10 a.m. and 4 p.m. and doesn’t significantly penetrate glass. Additionally, its intensity differs depending on how close to the equator you are.
It is important to note that UVB significantly affects birds’ eyes and many parrot owners have inadvertently caused their pet to have cataracts or blindness by misusing lights with UVB. In a study published by the Royal Society of Biological Sciences, a team of scientists studied a number of species of parrots that are commonly kept as pets and found that they possess UV-sensitive visual pigments (UVS). Consequently, their eyes are highly sensitive to UVB and overexposure can cause cataracts, macular degeneration, and blindness.
SUMMARY OF IMPORTANT FACTS ABOUT HOW NATURAL LIGHT WORKS
- Different wavelengths in the visible spectrum cause us to see different colors.
- The more wavelengths present in a light, the more natural an object looks.
- The measurement of a light’s color (K) is the final result of themix of the wavelength colors present in the light just like the final color of paint is a mixture of different colors.
- Wavelengths in the visible spectrum have no effect on the health of birds.
- Birds are not plants, their feathers do not act like leaves, therefore, natural light does notaffect bird plumage other than how it appears to the human eye.
- Birds can see UVA waves as well as the visible spectrum.
- UVA and UVB do not penetrate feathers.
- UVA has no known physical benefit to birds.
- UVB synthesizers, when absorbed by the skin, produce vitamin D3.
- 90–95% of UV radiation that reaches the Earth is UVA, which
- is present equally throughout the daylight hours and seasons and can penetrate clouds and glass.
- UVB makes up only 5–10% of solar radiation. It’s strongest between 10 a.m. and 4 p.m.and doesn’t significantly penetrate glass. Additionally, its intensity differs depending on how close to the equator you are.
- A number of bird species kept as pets possess UV-sensitive visual pigments (UVS). Consequently, their eyes are highly sensitive to UVB and overexposure can cause cataracts, macular degeneration, and blindness.
About the Author:
Mark Schack presents seminars on bird lighting at avian events around the country. Though without formal education in avian health, Mark is a mechanical engineer and lifetime hobbyist of breeding pet birds. Frustrated by the lack of availability of good lighting, he decided to build his own. The above information was gathered during Mark’s attempt to build “the perfect light” and through continued study of the subject.