Incandescence is a source of light that occurs naturally as well as artificially. In artificial applications, incandescence is produced by heating a filament in a light bulb until it glows. These incandescent filaments emit radiation across a broad spectrum, including infrared (heat) and some ultraviolet radiation. Only a small portion of this radiation falls within the visible range, which is perceived as light.

  • Incandescent light is produced when electricity flows through a filament, typically made of tungsten, heating it to thousands of degrees Celsius. This intense heat excites the atoms in the filament, causing them to change their energy levels and behaviour:
Energy Levels and Electrons
  • Atoms have distinct energy levels where electrons reside. Imagine these levels like steps on a ladder. The lowest energy level, called the ground state, is like the bottom step. Excitation occurs when atoms absorb energy, such as heat, causing their electrons to jump to higher energy levels (like climbing the ladder).
Energy Absorption and Excitation
  • The heat energy that causes excitation comes in the form of electromagnetic radiation, at visible light or infrared wavelengths. When the radiation collides with atoms, they can transfer their energy to the electrons. If the transferred energy matches the difference between two energy levels in the atom, the electron absorbs it and “excites” to the higher level.
Instability and Return
  • An excited atom is unstable and wants to return to its ground state. It does this by releasing the absorbed energy in different ways:
    • Light Emission: In many cases, the excited atom releases the energy as a photon (light particle) with a specific wavelength corresponding to the energy difference between the initial and final levels. This is how processes like incandescent light, neon signs, and some types of lasers work.
    • Collisions between atoms: The excited atom can transfer its energy to another atom through a collision. This can cause a chain reaction or lead to other physical or chemical reactions.
Colour and Efficiency
  • The colour of incandescent light depends on the filament temperature. Hotter filaments emit more bluish light, while cooler ones glow yellow or orange. However, incandescent light sources are generally less efficient than other lighting technologies, converting a significant portion of their energy into heat rather than light.
  • Incandescent light: In a hot gas, like the filament in an incandescent bulb, heating excites atoms, causing them to emit visible light, producing their characteristic glow.
  • Fluorescent Light: In fluorescent lamps, UV radiation excites atoms in a gas, the excited atoms then transfer their energy to other atoms, which in turn emit visible light.
  • Aurora: When sunlight excites atoms in the atmosphere, it causes them to emit specific wavelengths of light, resulting in phenomena like the aurora borealis.
Applications and Decline
  • While largely replaced by more efficient options like LED bulbs, incandescent lighting is still used in some applications due to its familiar warm glow and dimming capabilities.
  • However, its use is declining due to its lower energy efficiency and shorter lifespan.