Sectieoverzicht

    • Luminous and non-luminous objects

      Objects can be classified as either luminous or non luminous:

      • A luminous object is one which has its own source of light energy e.g. sun, stars and even some animals and plants. You are able to see luminous objects in the dark.
      • A non-luminous object is one which does not have its own source of light energy. Non-luminous objects reflect light from a luminous object. You cannot see non-luminous objects in the dark. Examples include the moon, planets, coal, cloth, houses and YOU! (Note that coal is non-luminous when it is not burning, when it is burning it is classified as a luminous object)



    • The moon

      Isn't it interesting that the moon is a non-luminous body. The moon does not emit its own light. We can only see the moon when it reflects the light from the sun.

      Image: Wikimedia Commons (CC BY)

    • Watch the short YouTube video below which clarifies what light is and the difference between luminous and non-luminous objects.

      meriSTEM Education. (2021). Light and luminous objects (CC BY)

    • Having now determined that objects can be classified as either luminous or non-luminous, let's dig a little deeper into the luminous objects.

      Light can come from a variety of sources but these sources can be categorised into one of the following viz.:

      • Natural light source e.g. sun
      • Artificial light source e.g. light bulb


    • Natural sources of light

      Some of the natural sources of light include the following:


      Click on the hyperlink below to find out more about these natural sources of light.


    • Natural sources of light Interactieve inhoud
      Leerlingen moeten
      Bekijken

    • Artificial light sources

      Artificial sources of light are mostly not natural sources of light, they are usually manmade objects which emit light (the exception being bioluminescent objects). Artificial light sources can be switched on and off whereas natural light sources can't.

      Artificial light sources can be divided into three categories:

      1. Incandescent sources
      2. Luminescent sources
      3. Gas discharge light source


      Let's look at each of these in a little more detail.

    • Incandescent light sources

      Certain objects can emit light when heated to a high temperature e.g. candles, firewood, electric lights and even gas lamps. 

      Electric lights emit light by the following process: the bulb filament converts electric energy to heat energy. The filament then becomes very hot and is able to then produce light. 

      Image: Pix (CC0)

    • Luminescent light sources

      Luminescent light sources are different to incandescent light sources since they do not produce heat when emitting light, they are non-incandescent.

      There are different types of luminescence, some of them being:

      Chemiluminescence: the emission of light is due to a chemical reaction which takes place e.g glow sticks and chemical experiments in the science lab
      Image: Wikimedia Commons (CC BY)


      Bioluminescence: some plants, insects and sea life are able to emit light via a chemical reaction which converts chemical energy into light energy e.g. bioluminescent clams, fire flies and glow worms. Note that these are natural sources of light and not artificial light
      Image: Flickr (CC BY)


      Electroluminescence       occurs when light is emitted as a result of the interaction of an electric field with a solid. A common example of this being car dashboard displays and head lights.
      Image: Wikimedia Commons (CC BY)

    • Gas discharge light sources

      Fluorescence: Florescent materials are able to absorb energy and then emit light e.g. fluorescent lights. The electricity causes the gas to emit ultraviolet radiation which stimulates the tube coating to emit light. When the energy is switched off, the lamp ceases to emit light.
      Image: Wikimedia Commons (CC BY)

      The main difference between fluorescence and phosphorescence is the time taken to emit light. Fluorescence is quicker to emit light and ceases to emit as soon as the energy source is cut. Phosphorescence will take longer to emit light and is able to continue to emit light even after there is a cut off of the energy supply e.g. safety signs, glowing paints.

    • Summary

      In this course you covered what light is and the different sources of light. In the next topic you will be learning about the propagation and transmission of light.

      To cement your knowledge on the sources of light, watch the YouTube video below which provides a clear summary of what has been covered in this course.

      Thereafter, complete the quiz to test your understanding of the sources of light.

      The K8 School. (2019). Sources of light (Standard YouTube licence)