- Written by Nadia O’Carroll
The basic design of aerial fireworks is a shell or casing with a timed fuse and bursting charge, within the shell is black powder which surrounds small pellets or packets of colourants known as pyrotechnic stars. When the shell is launched the fuse burns, ignites the bursting charge and explodes the shell scattering the pyrotechnic stars. How do these stars produce light and colour?
Visible light can be described as electromagnetic radiation that can be perceived by the human eye. The colours of the visible spectrum are red, orange, yellow, green, blue, indigo and violet (in order of longer to shorter wavelengths)
There are two basic types of light sources.
Incandescence is the release of electromagnetic radiation from an object as a result of heat and occurs when atoms are heated and release some of their thermal vibration as electromagnetic radiation.
The colour of the light released, the photon, depends upon the temperature. Because red is the lowest energy and longest wavelength of visible light it is the colour we first see when objects are heated, then orange, yellows until if
enough heat is applied a substance will glow white-hot. White light is not a colour but is a combination of all of the colours of the visible spectrum.
In fireworks incandescent light of gold, white and silver are produced by burning metals such as iron, magnesium, aluminium and titanium.
In nature sunlight, starlight and fire are examples of incandescent light.
Luminescence is the release of electromagnetic radiation from an object as a result of chemical, biochemical, or crystallographic changes, the motions of subatomic particles, or radiation-induced excitation of an atomic system. The effect of the cool energy source alters the orbital pattern of electrons in atoms.
When energy is absorbed by an electron of an atom or molecule, it moves into a high-energy state and orbits farther away from the atomic nucleus. When the electron falls back into its ground state it releases energy in the form of light. This is known as a photon and it produces light of a certain colour.
In fireworks luminescent light of red, orange, yellow, green, blue and purple is produced by chemical reactions between a range of compounds including strontium salts, lithium salts, calcium salts, sodium compounds, barium compounds, copper compounds and strontium compounds,
In nature luminescent light may be produced by a number of processes. Bioluminescent light is produced by chemical reactions in the cells of species such as glowworms, fireflies, fungi and marine creatures. Some gemstones, minerals and compounds exhibit phosphorescence.
Another example of natural luminescent light is the natural polar light display of Aurora Borealis and Aurora Australis. Unfortunately few people have the opportunity to witness what must be the most spectacular aerial fireworks display on Earth.