As humans, we have always identified the grass as green in color, mud as brown, sunflowers as yellow, sunsets as orange, and the list goes on. Light is the reason behind our ability to see these things and their diverse range of colors. Without light, the world would be in an eternal abyss of darkness.
Light is crucial for the survival of life forms other than humans. Plants, for example, need light for their various processes like photosynthesis. This light is provided by the sun. Thus, it can be said that sunlight is the primary source of light on Earth, but other sources of light do exist. This article will examine the different sources of light and the general category they belong to. However, to do so, the physical phenomenon of light itself needs to be understood clearly.
According to physics, light refers to electromagnetic radiation of different wavelengths, and it can be visible or invisible to the human eye. However, the light that humans see around them in the form of colors, illuminance etc., is called visible light. This light usually has a wavelength between 400 - 700 nanometers and has other important properties like frequency, intensity, propagation direction, speed in a vacuum etc.
Other than infrared and ultraviolet waves, the human eye can see almost all types of light. If the concept of light were to be explained in layman terms, it would be defined as a form of energy that takes the form of a wavelength and travels extremely fast.
The sun has always been the most important and necessary source of light for this planet. The biological clock inside our bodies is traditionally set to work alongside the movements of the sun. Historically another commonly used light source has been the fire. Ever since its discovery, fire has helped humans see during the night while simultaneously providing heat during the cold.
Humans also learnt how to create artificial forms of light around the 18th century BCE, thus no longer being completely dependent on the sun for all their visibility requirements.
The sources of light can be further broken down into categories according to their origin and properties. The main categories are presented below:
Light can originate from several different sources, but when it comes from objects that give light from naturally occurring sources and processes, it is often categorized as a natural light source. Many things occur naturally in nature and the universe that generates light, and listed below are a few sources that are commonly known or of use to humans.
The sun is the most important source of light for the Earth. It can be imagined as a massive ball of fire in which nuclear fusion generates an enormous amount of energy, producing the light we see.
Approximately 44% of the sunlight that reaches the Earth’s surface is visible to the naked human eye. Life on Earth depends on the light provided by the sun as the biological processes of most creatures are shaped around the amount of sunlight they receive. The sun also produces heat which has other uses on Earth.
Although the sun is also classified as a star, the stars referred to here do not belong to the solar system. Many distant stars produce light that reaches the Earth even though it is a small quantity.
Moon is a natural satellite that does not have its own light but reflects the sun's light.
Some living organisms produce their own light as a result of chemical processes within their bodies. Examples of such creatures include fireflies, jellyfish, glow worms etc.
Artificial light, which was developed during the 19th century, is made up of advanced technology and can be seen all around us in bulbs, tube lights etc.
This type of source includes the sun, fire and light bulbs. It basically refers to sources of electrical light that work by emitting light generated through heating.
This type of light is generated whenever an electron drop is seen in energy, and a specific light color is produced, like neon and fluorescent lights. Luminescence light is also referred to as cold light, as no heating is involved.