According to the Laws of Physics, light is just another form of energy that is obtained when electrons in the excited state fall back to their ground state. In addition to the light energy, there is the liberation of energy in the form of heat that takes place during the emission of light. But can there be light without heat? In this article, we will discuss the concept of light without heat.
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Can There Be Light Without Heat?
Yes, there can be light without heat. But this kind of light is known as cold-body radiation, unlike light from the regular bulb. In regular bulbs, the filament of the bulbs gets heated up and the outer electrons of the atoms get excited into the higher state. When these electrons come back to their ground state, they release energy in the form of light. Therefore, in regular light bulbs, there is light but it exists along with heat. On the other hand, the cold light is obtained as a result of chemical reactions, stresses on the crystal structures, and sub-atomic motions and operations.
What is Luminescence? (Cold Light)
Luminescence, also known as cold light or cold body radiations, is a phenomenon that occurs when an appropriate material absorbs energy from sources such as chemical reactions, X-rays, UV rays and so on. The valence shell electrons get excited to a higher state. But these higher states are short-lived and hence the electrons fall back to their ground state while releasing energy in the form of light. Luminescence is different from incandescence in the fact that incandescence arises from a hot body while luminescence is cold-body radiation.
9 Types of Luminescence (Light Without Heat)
1. Chemiluminescence
In fluorescent molecules, when the energy is used to excite electrons in a higher state during a chemical reaction, chemiluminescence occurs. The phenomenon of chemiluminescence is known to happen in the natural environment. But the intensity of the phenomenon is so low that sensitive detectors are necessary to observe its occurrence.
Compounds like luminol exhibit profoundly visible chemiluminescence. On oxidation, it produces a bluish or blue-greenish glow. Compounds like lucigenin and lophine also possess strong chemiluminescence. But not all compounds can reflect the phenomenon of chemiluminescence as noticeably as luminol. It is because only one percent of molecules and sometimes even less, emit the cold light.
2. Bioluminescence
Bioluminescence is a special case of chemiluminescence. It occurs as a catalyzed reaction in the presence of air. Also, the phenomenon of bioluminescence is greatly visible in all compounds because almost 100 percent of the molecules can emit light due to the presence of enzymes.
3. Triboluminescence
In the phenomenon of triboluminescence, the emission of light occurs due to the discharge of electrons during the crystallization process or mechanical disintegration of surfaces. For example, triboluminescence is clearly visible when adhesive tape is removed from the roll. The bluish glow that is seen by us is the light that is emitted from the nitrogen molecules of the air mixture. The nitrogen molecules are excited to a higher state due to the discharged electrons of the adhesive tape.
4. Thermoluminescence
Thermoluminescence is the phenomenon of increasing the luminescence of materials by enhancing the effect with the application of heat. In this phenomenon, the electrons which are already excited to the higher state are further excited by external heat. Thermoluminescence is highly visible in phosphor crystals.
5. Photoluminescence
Photoluminescence is the type of luminescence that happens when electromagnetic waves such as X rays, UV rays, and gamma rays fall upon the surface of the matter. It has been observed that the wavelength of the emitted light in the case of photoluminescence is generally equal to or higher than that of the exciting light. This is because the excited light is transformed into the vibrational energy of the molecules.
The application of photoluminescence can be seen in fluoroscopes and scintillation counters. The fluoroscope is used in X-ray diagnostics whereas scintillation counters are used in photomultiplier tubes.
6. Electroluminescence
The phenomenon of electroluminescence produces light on the virtue of several different processes. The light emission in electroluminescence takes place due to the electrical discharge. The natural lighting that happens in the atmosphere is an example of electroluminescence.
7. Radioluminescence
When radioactive elements emit particles such as electrons, gamma rays, and alpha particles, the phenomenon of radioluminescence exists. It means radioluminescence can be observed when radioactive elements that produce alpha particles are used to bombard an appropriate crystal structure. While doing so, certain scintillations are observed. Self-luminous paints which are used in watch dials are constructed on the principle of radioluminescence.
8. Crystalloluminescence
The emission of light in crystalloluminescence takes place during the crystallization process of small pieces of crystal.
9. Fluorescence
In this phenomenon, certain fluorescent materials absorb light and illuminate for a while. Fluorescence is short-lived. The electric current running from fluorescent light bulbs creates electrons while passing through the mercury. These electrons then strike upon the surface of the bulb and create luminescence.
Examples of Natural Luminescence
- Angler fishes have bacteria that exhibit the phenomenon of bioluminescence to attract prey.
- Comb jellies use bioluminescence to ward off predators. Any bite by the enemy keeps glowing to make it more visible.
- Fireflies have a reaction going on inside their bodies. By virtue of this chemical reaction, luciferin is changed into a different form. This reaction releases energy in the form of luminescence.
- More than 70 species of fungi use bioluminescence as a way of reproduction. The glowing fungi attract predators which help to scatter the spores of fungi.
- Dinoflagellates like plankton use bioluminescence to guard against predators.
- Sea Worms have a distracting mechanism for predators. They create little parcels of liquid that opens and creates luminescence for some time to startle the catchers.
Conclusion
There are plenty of example of luminescence, or light without heat. Light bulbs work by heating the filament causing the electrons to light up. In nature, chemical reactions, stresses on the crystal structures, and sub-atomic motions and operations can cause things to light up without any heat.