Light is all around us. The Sun shines on the Earth every day and we use electric lights or candles to light our homes, schools and workplaces. We use torches or streetlights when we are out and about at night and build fires for light and warmth when we go camping. Even in the middle of the night, there is some light from the stars in the sky.
But one of my daughter’s schoolfriends asked me how light is made. And her brilliant question made me think about natural and man-made light sources.
So, let’s find out more about light – what it is and how it is made…
Light is a kind of energy that travels in straight lines, called ‘waves’. These waves can be of different lengths and contain different amounts of energy – the longer the wavelength, the lower the energy. Scientists arrange these waves from longest to shortest wavelength in something called the electromagnetic spectrum. Our eyes can see some of these waves and we call this ‘visible light’. But we can’t see other kinds of waves in the spectrum because the wavelengths are too long or too short for our eyes to see them.
The Earth gets light from the Sun, which is a big star at the centre of our solar system. As I explained in why is the Sun hot?, inside the Sun hydrogen is being turned into helium making huge amounts of energy. This energy is released as light and heat, which we can see and feel from more than 90 million miles away! So, the Sun makes light (and heat) energy from a massive chemical reaction.
But what about the lights that we have in our homes, schools and other buildings? These lights are powered by electricity. In lightbulbs, electricity flows along a thin wire called a ‘filament’. The flow of electricity heats the filament until it gets hot and gives out heat and light energy which glows a sort of yellowy-white colour.
And don’t forget the brightly coloured neon signs that you sometimes see at night on shops and outside other buildings. They are also powered by electricity but instead of heating up a wire filament, the electricity puts energy into the neon gas inside a lighting tube. The electricity makes the neon atoms bump into each other, releasing energy that we see as light.
So, light is a kind of energy that can be made by chemical reactions or by heating things up! And if you want to find out more about light and how it works, try this video.