What is light, how does it spread and what are its types

What is light?

The nature of light is very complex. It is therefore not surprising that the greatest scholars of their time could not agree on it. René Descartes and Isaac Newton thought it was a stream of particles smaller than atoms. Robert Hooke and Christiaan Huygens saw it as a wave. In the end, both camps were right. Light is both at the same time.

Sometimes it behaves like a block of tiny particles that we call photons. They have no mass and are the only particles in the universe that can travel at the highest possible speed. The speed of light. Other times, it's like a wave with its own frequency and wavelength. This phenomenon is known as light dualism.

So, from a physical point of view, light is transverse electromagnetic waves of a narrow wavelength region, which also manifest as a flow of photons. And because photons enable the transmission of electric and magnetic forces, we can also call light electromagnetic radiation.

How does light spread?

However, the final resolution of the question of light propagation from the point of view of classical physics did not come until the 19th century, when the so-called Huygens principle came into force. According to this principle, light propagates by means of wavefronts. Every place the wave reaches becomes the centre of an elementary spherical wave. And the resulting wavefront is the envelope of the elementary wavefronts.

Light sources

Light is propagated by light sources. This is the name given to any body in which light originates and from which it emanates into the surroundings. We divide them into natural and artificial.

Natural sources include, for example, the sun, stars, the moon, fire, lightning and glowing lava. Artificial, i.e. man-made, includes light bulbs, fluorescent lamps, discharge lamps or light-emitting diodes.

Optical environment

The propagation of light is also affected by the properties of the optical environment, i.e. the medium in which it occurs. This can be:

• Transparent
  A transparent optical medium transmits light without significant attenuation so that we can see through it.
  
  
• Opaque
  An opaque environment does not transmit light; it absorbs or reflects it, so we cannot see it.
  
  
• Translucent
  A translucent environment lets light through but scatters it in all directions, causing us to see only some of it.

What are the types of light?

Light is far from just what we see with our eyes. What forms can it take? And what are they good for? Let's take it one step at a time. Starting with the longest wavelength.

Radio waves and microwaves

Electromagnetic waves larger than 1 mm are referred to as radio waves and microwaves. The former transmit, for example, TV, radio or wi-fi signals, while the latter are used in ovens and radar. Wi-fi networks and microwave ovens have almost the same frequency, which is why your internet can sometimes slow down while your food is heating up.

Infrared radiation

Infrared radiation has waves smaller than 1 mm. This is emitted by all heat sources. So do people. That's why with an infrared camera you can see all living things even in complete darkness. Near-infrared light in the 700 to 1000 nm range is widely used in regeneration. It penetrates deeper into the body and has a healing effect on the tissues, thereby promoting muscle health and the body's recovery processes. Mid- and far-infrared light is contained in infrared saunas.

Visible light

Wavelengths in the range of 380-740 nm are called visible light. This part of the electromagnetic spectrum produces visual sensation when it hits the photoreceptors of the human eye. These are the so-called spectral colours - red, orange, yellow, green, cyan, blue, violet.

The same color as the rainbow. And even in the same order, because the rain breaks down the sunlight into individual colours according to wavelengths. But there are also non-spectral colours (white, grey, black, pink, turquoise) which are created by mixing the spectral ones.

UV radiation

We can't see waves below 380 nm again. The violet colour transitions smoothly into UV, with UltraViolet meaning "above violet". This light can already be dangerous to a greater extent. That's why we apply sunscreen and protect our eyes with UV-filtered sunglasses. Interestingly, birds and reptiles can see this light, so they can easily read messages written in invisible ink. :-) But the rest of us need special tools to do this.

X-rays

Electromagnetic waves below 10 nm are known as X-rays, which are used to scan the human body for possible fractures and breaks. The reason for this is simple - it contains a lot of energy, which means it can pass through things that ordinary light cannot. Like soft tissue. It hits the bones and bounces off them, so we can see the detail of the skeleton in the resulting images.

Gamma rays

Waves smaller than 10 pm are known as gamma rays. Their frequency is only slightly smaller than the diameter of atoms and they are produced, for example, during radioactive decay, when the nucleus of an atom needs to get rid of excess energy. Gamma rays are extremely dangerous and only a really, really thick layer of lead will provide sufficient protection against them. This includes cosmic radiation, which can be produced during a nuclear explosion, but fortunately this danger is pacified by the atmosphere, so we are not in danger.

Discover the beauty of light

We often take light for granted, even though it is one of the most precious commodities in the universe. It gives us life, health, information, entertainment, happiness and the opportunity to experience the beauty of the world around us. Discover it for yourself. In its crystal clear form.