A light-emitting process refers to any physical mechanism by which a material emits light. These processes involve the transformation of energy within a material into electromagnetic radiation, which includes visible light.
- There are several ways in which materials can emit light, leading to different light-emitting processes. Here are some of the primary categories:
Luminescence
Light is produced when excited electrons within a material drop back to a lower energy state, releasing energy in the form of light. This category includes:
- Photoluminescence (excitation by light absorption)
- Electroluminescence (excitation by an electrical current)
- Chemiluminescence (excitation by a chemical reaction)
- Bioelectroluminescence (excitation through biological processes in living organisms)
- Thermoluminescence (excitation by heat)
- Sonoluminescence (excitation by sound waves and collapsing bubbles)
- Triboluminescence (excitation by mechanical stress)
Thermal Radiation
- Light is produced due to the thermal motion of atoms and molecules. Any object above absolute zero emits thermal radiation, including a portion in the visible light spectrum.
Nuclear Reactions
- Light is produced as a byproduct of nuclear processes like fission (splitting atomic nuclei) and fusion (combining atomic nuclei).
Blackbody Radiation
- A specific type of thermal radiation emitted by a perfect ‘blackbody’. The spectrum and intensity of blackbody radiation are determined solely by the object’s temperature.
Understanding Light-Emitting Processes
- Energy transformation: Light emitting processes involve various forms of energy transformation, such as the conversion of electrical energy, chemical energy, thermal energy, or mechanical energy into light energy.
- Material properties: Specific properties of different materials determine the type of light-emitting process they can undergo.
- Applications: Understanding different light-emitting processes has numerous applications in fields like lighting, displays, medicine, and scientific research.
| Light sources | Emission mechanism | Description | Examples |
|---|---|---|---|
| LIGHT-EMITTING PROCESS | |||
| Luminescence | Light emission due to the excitation of electrons in a material. | Electrons within a material gain energy and then release light as they return to a lower energy state. | Bioelectroluminescence Electroluminescence Photoluminescence - Fluorescence - Phosphorescence Sonoluminescence Thermoluminescence |
| Blackbody radiation (Type of thermal radiation) | Electromagnetic radiation (including visible light) emitted by any object with a temperature above absolute zero. | Electromagnetic radiation (including visible light) emitted by any object with a temperature above absolute zero. | All objects above temperature of absolute zero. |
| Chemiluminescence | Light from natural and artificial chemical reactions. | Light from natural and artificial chemical reactions. | Bioluminescence Chemiluminescent reactions: - Luminol reactions - Ruthenium chemiluminescence |
| Nuclear reaction | Light emission as a byproduct of nuclear reactions (fusion or fission). | Light emitted as a byproduct of nuclear reactions. | Nuclear reactors Stars undergoing fusion |
| Thermal radiation | Light emission due to the thermal excitation of atoms and molecules at high temperatures. | Light emission due to the thermal excitation of atoms and molecules. | Sun Stars Incandescent light bulbs |
| Triboluminescence | Light emission due to mechanical stress applied to a material. | Light emission due to the mechanical stress applied to a material, causing the movement of electric charges and subsequent light emission. | Sugar crystals cracking Adhesive tape peeling Quartz crystals fracturing. |
| Natural light source | |||
| Fireflies Deep-sea creatures Glowing mushrooms | Bioluminescence | Light emission from biological organisms. | Involves the luciferase enzyme. |
| Sun Stars | Nuclear Fusion | Light emission as a byproduct of nuclear fusion reactions in stars. | Electromagnetic spectrum (visible light, infrared, ultraviolet). |
| Fire Candles | Thermal radiation | Light emission due to the thermal excitation of atoms and molecules during the combustion of a fuel source. | Burning of a fuel source, releasing heat and light. |
| Artificial light source | |||
| Fluorescent lights Highlighters Safety vests | Chemiluminescence | Light emission from chemical reactions. | Fluorescence (absorption and re-emission of light). |
| Glow sticks Emergency signs | Chemiluminescence | Light emission due to phosphorescence - a type of chemiluminescence. | A type of chemiluminescence where light emission is delayed after the initial excitation. |
| Glow sticks Light sticks | Chemiluminescence | Chemiluminescence | Light emission from a chemical reaction that does not involve combustion. |
| Tungsten light bulbs Toasters | Thermal radiation | Heated filament radiates light and heat. | Light emission from a hot filament. |
| Fluorescent lamps LED lights | Electroluminescence | Excitation of atoms by electric current. | Light emission when electric current excites atoms in a material. |
| Neon signs | Electrical Discharge | Discharge of electricity through gas. | Light emission when electricity flows through a gas. |
| Sugar crystals cracking Pressure-sensitive adhesives | Triboluminescence | Light emission from friction or pressure. | Light emission due to mechanical forces. |
| Fluorescent paint Highlighters Safety vests | Photoluminescence | Absorption and subsequent re-emission of light at a lower energy. | Absorption and re-emission of light. |
Light Sources: Mechanism, examples, and everyday applications
Footnote: Cerenkov radiation and Synchrotron radiation are not included in the table because they are not conventionally classified as light sources.
- A light-emitting process refers to any physical mechanism by which a material emits light. These processes involve the transformation of energy within a material into electromagnetic radiation, which includes visible light.
Luminescence
Light is produced when excited electrons within a material drop back to a lower energy state, releasing energy in the form of light. This category includes:
- Photoluminescence (excitation by light absorption)
- Electroluminescence (excitation by an electrical current)
- Chemiluminescence (excitation by a chemical reaction)
- Bioelectroluminescence (excitation through biological processes in living organisms)
- Thermoluminescence (excitation by heat)
- Sonoluminescence (excitation by sound waves and collapsing bubbles)
- Triboluminescence (excitation by mechanical stress)
Thermal Radiation
- Light is produced due to the thermal motion of atoms and molecules. Any object above absolute zero emits thermal radiation, including a portion in the visible light spectrum.
Nuclear Reactions
- Light is produced as a byproduct of nuclear processes like fission (splitting atomic nuclei) and fusion (combining atomic nuclei).
Blackbody Radiation
-
- A specific type of thermal radiation emitted by a perfect ‘blackbody’. The spectrum and intensity of blackbody radiation are determined solely by the object’s temperature.