Emitted light refers to light that is produced and given off by a source, rather than light that is reflected or transmitted. This light is a form of energy that travels as electromagnetic waves, but it can also be understood as discrete packets of energy called photons. Light’s presence shapes how we experience the world, from the glow of a screen to the warmth of the sun. It is a fundamental phenomenon that underpins our visual perception and countless technological advancements.
The Science of Light Emission
Light originates at the atomic level, where electrons orbit the nucleus in distinct energy shells or levels. Electrons naturally reside in their lowest possible energy states, referred to as the ground state, much like a ball resting in a valley. When an atom absorbs energy from an external source, such as heat, electricity, or chemical reactions, its electrons can become “excited.” This added energy causes them to jump to higher, less stable energy levels.
An electron in an excited state will only remain there for a very short duration. It then seeks to return to a lower, more stable energy level, analogous to the ball rolling back down the hill. As the electron transitions from a higher energy state to a lower one, it releases the excess energy in the form of a photon. The specific energy difference between the electron’s initial and final energy levels dictates the energy of the emitted photon, which in turn determines the light’s wavelength and color. Each element possesses a unique set of energy levels, resulting in distinct patterns of emitted light.
Common Types of Emitted Light
Different forms of energy input lead to various types of light emission, each with distinct characteristics.
Incandescence
Incandescence is the emission of light due to heat. When a material like the tungsten filament in an incandescent light bulb is heated to extremely high temperatures, often exceeding 2,200 degrees Celsius (4,000 degrees Fahrenheit), its atoms become thermally excited. This excitation causes them to emit photons across a broad spectrum, producing the familiar warm glow. Fire and molten metal are other examples of incandescence.
Luminescence
Luminescence encompasses light emission not primarily caused by heat.
Fluorescence
Fluorescence is a type of photoluminescence where a substance quickly absorbs light, typically ultraviolet radiation, and then re-emits it almost immediately as visible light of a longer wavelength. Fluorescent lights and certain bright paints exhibit this effect, ceasing to glow almost instantly when the energy source is removed.
Phosphorescence
Phosphorescence is similar to fluorescence but involves a slower re-emission of light. Here, absorbed energy causes electrons to transition to an excited state from which they return to the ground state more slowly. This results in a persistent afterglow that can last from microseconds to several hours after the light source is removed. Glow-in-the-dark toys and emergency exit signs often utilize phosphorescent materials like strontium aluminate.
Electroluminescence
Electroluminescence occurs when a material emits light in response to an electric current or a strong electric field. This phenomenon is commonly observed in Light Emitting Diodes (LEDs), where electrons and “holes” recombine in a semiconductor material. This converts electrical energy directly into light with minimal heat generation. This mechanism is also used in some display backlighting.
Chemiluminescence
Chemiluminescence involves light production from a chemical reaction, where the energy released by the reaction excites molecules to a higher energy state, and subsequent relaxation leads to photon emission. An example is the glow stick, where mixing chemicals initiates a light-producing reaction. Bioluminescence is a specific type of chemiluminescence occurring in living organisms, such as fireflies and certain deep-sea creatures.
Everyday Applications
Emitted light plays an expansive role in our daily lives and various technological advancements.
Illumination
LEDs and fluorescent bulbs provide energy-efficient lighting for homes, offices, and streets. These modern light sources have largely replaced older incandescent bulbs due to their efficiency and longer lifespan.
Displays
Displays in televisions, smartphones, and computer screens use emitted light, particularly through LED and OLED (Organic Light Emitting Diode) technologies. LEDs provide backlighting for many liquid crystal displays, offering improved contrast and reduced power consumption. OLEDs are self-emissive, meaning each pixel produces its own light, allowing for thinner displays and deeper blacks.
Communication
Communication systems leverage emitted light. Fiber optic cables transmit data as light pulses, enabling high-speed internet, telephone conversations, and television broadcasts over long distances. Remote controls utilize infrared light-emitting diodes to send signals to electronic devices. Laser pointers, which emit coherent light, are used for presentations and various alignment tasks.
Medical Field
In the medical field, emitted light has many applications. Lasers are used in precise surgical procedures, such as vision correction and tumor removal. Phototherapy, using specific wavelengths of light, can treat skin conditions like psoriasis and jaundice in newborns. Diagnostic tools also employ light, such as endoscopes to visualize internal organs or pulse oximeters to measure blood oxygen levels.
Safety and Security
Emitted light contributes to safety and security. Emergency lighting systems, often powered by phosphorescent or electroluminescent materials, provide illumination during power outages, guiding people to safety. Optical sensors that detect light emitted from flames are used in fire alarms and gas burner monitors for early hazard detection.