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A motivation to improve the efficiecy of Light sources Fire-fly was a motivation to improve the efficiency of light sources! Fireflies produce light through a chemical reaction that takes place in its specialized cells. Light travels through the fluid medium (inside the insect) more slowly than it travels through air. This led to discovery of minimized internal reflections which produces more light. Thus an existing light source can be modified to increase its efficiency. Let us know the other sources of light and its properties.

Learning objectives

After completing the topic, the student will be able to:

  • Discover the dual nature of light and illustrate it based on simple experiments.
  • Understand the phenomenon of Photoelectric effect using simple experiments.
  • Discover the ideas like De Broglie′s hypothesis, Uncertainty principle, which lead to the birth of quantum mechanics.
  • Distinguish clearly between light and sound waves.
  • Explore the nature and components of electromagnetic spectrum.
  • Discuss various sources of light and their significance in daily life scenarios.
  • Discover the evolution and importance of monochromatic beams(LASERS) and their significance in medicine and applied physics.
  • Examine why shadows are formed, understand their characteristics and relate to the study eclipses.
Morning rays Rays of light beam through the trees on a cool morning.A
Nature of light

First thing we can say about light is that it is something that enables us to see. But what is light? We know that during the day the primary source of the light is the sun, and the secondary source is the brightness of the sky. Other common sources are flames, white–hot filaments in light bulbs and glowing gas in glass tubes. Light is a form of energy, which enables us to see objects from which it comes. We detect light by our eye, which is an optical instrument provided to us by nature. Light can be transmitted from one place to another at finite velocity.

Light energy originates somewhere within an atom and ends its existence, when it enters another atom or molecule. All light originates from the accelerated motion of electric charges. Light is an electromagnetic phenomenon; visible light is a tiny part of a larger electromagnetic spectrum of radiation ranging from cosmic rays to radio waves. Understanding the nature of light, the emission and absorption processes are very important.

Sources of light Light from the Sun is the natural source for all other energies. Light sources such as incandescence, fluorescence and phosphorescence are artificial light sources.
Sources of light

Our primary source of light is the Sun. But there are other man made light sources as well. A source of light can be classified into one of the three categories given below:

  • Incandescence (thermal sources): These sources contain light of all wavelengths in the visible region.
  • Fluorescence: This source contains light of few wavelengths as in a gas discharge tube.
  • Phosphorescence: This source contains partly visible light and partly ultraviolet. In this, light is emitted by the principle of luminescence, which is the phenomenon of emission of light by a substance, by absorbing suitable electromagnetic radiation.