Since we sometimes take the light from the sun for granted, without it, the earth would be lifeless. Plants would not be able to grow and consequently animals and humans would be left without food. Sunlight is the main source of energy on earth and if this grows dim, the world would turn cold and water would freeze.
In order to understand light in its entirety as well as its sources, we need to look at how it works and its effects.
Understanding Light and How It Moves
Light is basically a form of energy given off when something burns. For instance, the sun is a ball of burning gases which in turn gives off light. Light travels in ripples just like waves in a pond. They travel through the air at a speed of 300,000 kilometers per second. This means light from the sun reaches us in approximately 8 minutes as the distance between the earth and the sun is about 150 million kilometers.
Light travels in straight lines known as rays. Each light wave consists of different wavelengths and this is what gives us the colors of light.
The sun is the main source of natural light. Explosions happening at the center of the sun produce huge amounts of energy which is then released as heat and light. Some of this energy reaches the earth while part of it gets absorbed in the atmosphere. The light from the sun is referred to as white light.
In addition to the sun, natural light also comes from the stars. Because of the distance from the earth, light from the stars constitutes a small percentage of the total light reaching the earth. The moon is never a source of light but a reflector of light from the sun.
Some animals have the capacity to produce their own light. This is called bioluminescence. The light from these animals is mainly used to attract other creatures.
Human beings through scientific inventions have managed to create and control light. The earliest recognizable form of lighting used by man was fire. This came from burning wood and later gas, oil, and candles. Candles are made from tallow or beeswax. Electricity has now taken over as a convenient source of artificial light.
Electricity as we know it today was developed in the 19th century by Thomas Edison and Joseph Swan. These two scientists designed the first electric light bulbs which had a carbon thread known as a filament that glowed when electricity flowed through it.
The common types of electric lights include neon lights, fluorescent tubes, and tungsten filament light bulbs.
Tungsten filament bulbs are the cheapest of the three and contain a thin metal filament made from tungsten which becomes hot when an electric current flows through it. The yellow-white glow is what gives light.
Neon lights on the other hand, are commonly used in advertisement. Neon is an inert gas that gives light whenever high voltage electricity is passed through it. Different colors can be produced by simply varying the electric current.
Fluorescent tubes are mainly used in homes and offices. The tubes contain mercury vapor which gives off UV light whenever electric current is passed through it. The UV light is then absorbed by the phosphor powder which coats the inner part of the tube. This results into a glow that produces blue white light.
These are the only known sources of light, but with scientific inventions in top gear, only the future can tell what more will be added.