Light is electromagnetic radiation. In addition to visible light, electromagnetic radiation also includes gamma radiation, x-ray radiation, ultraviolet radiation, infrared radiation, microwave radiation and radio radiation. Individual types of radiation differ from each other by the wavelength (see figure).

Pic 13: Wavelength

Radio waves

It is interesting to note that, for example, radio waves have a wavelength that can be compared to large buildings and can reach one kilometer in length. In radio waves, we distinguish between smaller and larger wavelengths, which we know from ordinary life, such as long, medium, short, very short waves (VHF, or Very High Frequency VHF) and ultra-short waves (Ultra High Frequency UHF). Very short radio waves have much smaller wavelengths than long radio waves, but only in comparison to the macro-wave (from kilometers to centimeters). For example, in comparison with light radiation, the difference between long and very short radio waves is negligible. It is also interesting to note that microwave radiation,such as that used in microwave ovens, has wave sizes in several millimeters (0.01m) and therefore does not affect materials at the molecular level.

Like radio waves, light rays consist of waves of varying wavelengths, with the human eye perceiving the light spectrum of a certain wavelength as a certain color of light:

Pic 14: Radiation of light spectrum
(Picture source:

The visible light

The part of the radiation that one can perceive is called visible light. Some animals are able to see radiation in other areas of the spectrum, for example, a bee sees ultraviolet light that one cannot see, and some reptile species can see infrared light, which one cannot see by his eyes.

All of the light wavelengths together give white light – one perceives it as colorless. Light can be divided in different ways according to different wavelengths, which one perceives as a color spectrum (the formation of a rainbow). This means that it can visually find out what light wavelength is based on what color it manifests. For example, if we cover a glass that passes all the visible light wavelengths through a red foil, only the wavelength of light we see as a red light gets behind the glass. At the same time, this means that the film has the property of capturing the remaining light spectrum colors. If the object appears red, it means that it only reflects red light, the other parts of the light spectrum are absorbed by the material. The more light the material absorbs, the more it warms – the light is absorbed in the materials into heat. The greatest source of light on Earth is the Sun (star of the Solar System). The light from the sun will reach Earth in about 8 minutes. On Earth, light is absorbed by various materials and transformed into heat.

Light and shadow

The light travels through the space in a straight line from the source in all directions, unless it is directed. If light falls on different materials, it can be absorbed, reflected or refracted. These phenomena give rise to shadows. Light from the source travels straight to the object. If the object is not translucent, part of the light will be absorbed and part will be reflected. Only the light for which the object is not an obstacle goes beyond the object. Since the light travels through the space in a straight line, sometimes the same object is for light and sometimes a smaller obstacle. Therefore, if we shine on an object at a different angle, the length of the shadow that is created behind the object changes. This phenomenon is observed during the day and during the year due to the apparent movement of the sun in the sky.

Pic 15: Light and shadow

All objects create shadows that capture at least part of the light. However, light must flow around the object, otherwise the shadow is not created. The shadow is therefore the place behind the object where there is less light than around. Shadows can also be colored if they are created behind an object that permits part of the light and is also colored. Light can vary in intensity. Some light sources provide very little light, others emit very intense light. The more light sources shine on a certain space, the more intense the light in the space is. For this reason, we can see lighter and darker shadows.

Reflection of light

One sees objects because light reflects of them. Since the light travels in a straight line , we cannot see objects that are behind the corner. We can only see an object on which the light is falling, and at the same time the light is reflected in our eye. As all objects on Earth reflect at least part of the light, they are visible to us. If the object were to absorb all the light, it would be invisible to the human eye. Invisible things become objects in the absence of light – in the dark. Even animals that are adapted to the nightlife and use sight for orientation in the environment cannot see anything in the complete absence of light (for example, a cat). However, with low light intensity, these animals can also see objects that no one can see. That is why we are talking about man as an animal adapted to the daily way of life. For this reason, man has a natural respect for darkness from birth.

By reflecting light, it is possible to change the direction of its journey. Reflection of light from objects has its patterns. The angle at which the light falls on the object is reflected at the same angle. In the mirror we see ourselves because it reflects a very large amount of light due to its smooth surface. For example, we can see your reflection in a flat aluminum foil. However, if we shrug it, the image is lost. It also works when you see your reflection on the water surface. While the water level is peaceful, we see our reflection. When the water level is clearing, the image is lost.

Pic 16: Reflection of light

Travelling of the light

Light travels through vacuum, translucent and transparent materials. Light travels in the vacuum the fastest. It travels differently in different materials. When light passes from one material to another, it breaks at its interface. This phenomenon can be observed, for example, when light passes from air to water. Light spreads through the air faster than water or glass. When the light beam comes out of the air into the water, the light spreads below the water more slowly than above the water and we say the light beam breaks. Because of this phenomenon, one perceives objects that he observes from the air in the water in a different position than they actually are (see pictures).

Pic 17: Travelling of the light
(Picture source:

If we want to catch a coin from the bottom of a container, for example, we cannot precisely determine its location because the light that indicates its position breaks at the water-air interface. However, if we dip our eyes in water, we can locate the coin exactly. Although the light is spreading at different speeds in the water, it is still straightforward.