What is Light? (may2020)
The Power of Light
Light is a form of energy that illuminates our world. From ember-red autumn leaves, to white snow-covered mountains, to the glowing colours of a sunset – our eyes have become capable of seeing these beautiful sights because of light.
So, what exactly is light?
Light is a form of energy, usually produced by matter. The building blocks of matter are atoms, which has a nucleus that is surrounded by electrons. The nucleus holds a positive charge, while electrons are negatively charged. The electrons will normally remain at the same average distance from the centre of the atom. However, the theory of quantum mechanics allows this distance to change. When this happens, the electron may find itself closer to the nucleus, which also implies that it carries less energy. This energy reduction causes an equal amount of energy to be released as a photon: a particle that has no mass and moves at the speed of light. When a photon interacts with matter, it does so as a wave – known as electromagnetic waves, as it displays both electrical and magnetic components. In everyday terms, photons and electromagnetic waves are light.
How do we see light?
As light moves through space, it reaches the back of our eyes, where the photos are converted to electrical signals that are then processed by our brain. Our brain detects the appearance, location and movement of the object we are looking at. This type of light is known as visible light, which is the visible part of the electromagnetic spectrum detected by the human eye.
Objects we see are either luminous or non-luminous. Luminous objects generate their own light, like the sun. Non-luminous objects reflect light generated from other objects to our eyes, allowing us to see things such as a yellow banana. Without luminous objects generating light, non-luminous objects cannot be seen.
Objects interact with light in three different ways:
- Transparent materials – light travels through, which is why we are able to see across.
- Rough, opaque materials – most of the light is absorbed and changed into heat energy
- Smooth, shiny materials – light bounces off in one particular direction.
Many objects exhibit a combination of the above behaviors.
How do we see colour?
Typically, white light (for example, light from the sun) shines on a non-luminous object. The object will reflect certain colours and absorb all others. The colour of an object is the colour of light it reflects; an apple appears red because it reflects the red colour of light, absorbing all others.
How fast is the speed of light?
Light travels at 299,792,458 kilometers per second. To put that into perspective, the circumference of the Earth is approximately 40,000 kilometers; in one second, light can travel around the Earth seven and a half times.