Atoms and light photons. Photon absorption and emission

07/05/2026

The online atoms and light photons simulations on this page illustrate in an interactive way what the relationship between atoms and light photons is like and what the photon absorption and emission processes are like at the atomic level.

This Thematic Unit is part of our Chemistry collection

Atom-Light Interaction

Physical process through which an atom’s electrons absorb or emit radiant energy in the form of photons.

Electronic Transition

Displacement of an electron between two allowed energy levels, mediated by the absorption or emission of a photon.

Energy Quantization

Principle stating that electrons can only exchange energy in specific, discrete amounts.

Excited State

Condition of an atom after absorbing energy, where an electron occupies a higher energy orbital than the ground state.

Ground State

Lowest and most stable energy level in which an electron can be found within an atom.

Line Spectrum

Series of discrete lines representing the specific frequencies of light emitted by excited gaseous atoms.

Photon

Quantum of electromagnetic radiation representing the minimum unit of interaction between light and electrons.

Spontaneous Emission

Process by which an electron in an excited state returns to a lower level, releasing a photon without external intervention.

Relationship between atoms and light photons

Light at the atomic level is a complex phenomenon that can be understood as either a wave or a particle.

As a wave, light is an electromagnetic wave. Electromagnetic waves have a frequency and a wavelength that determine their energy and color. Visible light is only a small part of the electromagnetic spectrum, which also includes radio waves, microwaves, X-rays and gamma rays, among others.

As a particle, the study of light starts with photons, which are the elementary particles of light.

Absorption and emission of light photons at the atomic level

The absorption of light by an atom can cause an electron to jump to a higher energy level, while the emission of light by an atom occurs when an electron falls from a higher to a lower energy level and emits a photon. This process is known as electronic transition and is controlled by the laws of quantum mechanics.

Each electron jump produces a light photon of specific energy, which determines the color of the light that is emitted. For example, when electrons in a hydrogen atom jump from energy level n=3 to energy level n=2, a photon of red light with a specific wavelength is emitted. If electrons jump from the n=2 level to the n=1 level, a photon of blue-green light with a different wavelength is emitted. This process is known as electronic transition and is controlled by the laws of quantum mechanics.

Atom-Light Interaction

Physical process through which an atom’s electrons absorb or emit radiant energy in the form of photons.

Electronic Transition

Displacement of an electron between two allowed energy levels, mediated by the absorption or emission of a photon.

Energy Quantization

Principle stating that electrons can only exchange energy in specific, discrete amounts.

Excited State

Condition of an atom after absorbing energy, where an electron occupies a higher energy orbital than the ground state.

Ground State

Lowest and most stable energy level in which an electron can be found within an atom.

Line Spectrum

Series of discrete lines representing the specific frequencies of light emitted by excited gaseous atoms.

Photon

Quantum of electromagnetic radiation representing the minimum unit of interaction between light and electrons.

Spontaneous Emission

Process by which an electron in an excited state returns to a lower level, releasing a photon without external intervention.

Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!

Atoms and light photons simulations

Neon lights and other discharge lamps

Produce light by bombarding atoms with electrons. See how the characteristic spectra of different elements are produced and configure the energy states of your own element to produce light of different colors.

Screen too narrow

This Java simulation cannot run on this device because it has a screen that is too narrow. We recommend that, for a better user experience, you run it on a device with a wider screen.

Narrow screen

Although this Java simulation can be run on your device, we recommend that for the better user experience, you run it on a device with a wider screen.

Absorption and emission of light

Electrons can change position by receiving energy (mainly light energy). The atom absorbs the incoming energy and returns it to its surroundings in the following order. Electrons that have risen to a high level drop back to their original position. At that time, they emit light photons.

Quantum of light

Move the arrow and observe how the wavelength, energy and emitted photons change.

</div

Giants of science

“If I have seen further, it is by standing on the shoulders of giants”

Isaac Newton

Robert Boyle

1627

–

1691

Robert Boyle formulated the first quantitative law of gases, showing the relationship between pressure and volume, laying foundations of modern chemistry and fluid mechanics

“Air is as necessary to life as food”

Gilbert Newton Lewis

1875

–

1946

Gilbert Lewis formulated the chemical bond theory, introduced electron pairs, and contributed to acid-base theory

“Atoms build nature as bricks build a building”

Become a giant

Your path to becoming a giant of knowledge begins with these top free courses

Free mode

The Physics of Electronic Polymers (PEP)

Free mode

Energy to Electrochemistry Final Exam

Free mode

Electrochemistry

Free mode

Big Bang and the Origin of Chemical Elements

Free mode

Pre-University Chemistry

Free mode

Preparing for CLEP Chemistry: Part 1

Professional development for Educators

Your path to becoming a giant of knowledge begins with these top free courses

Free mode

Teach kids computing: Developing your programming pedagogy

Free mode

HP Digital Skills for Educators – Google Workspace

Free mode

Teach computing: Introducing physical computing

Free mode

Teaching Science and Engineering

Giants of science

“If I have seen further, it is by standing on the shoulders of giants”

Isaac Newton

Amedeo Avogadro

1776

–

1856

Amedeo Avogadro stated his famous hypothesis: equal volumes of gases, under the same conditions, contain the same number of molecules. He grounded modern chemistry and molecular theory

“In science, patience and method always triumph over chance”

Gilbert Newton Lewis

1875

–

1946

Gilbert Lewis formulated the chemical bond theory, introduced electron pairs, and contributed to acid-base theory

“Atoms build nature as bricks build a building”

Become a giant

Your path to becoming a giant of knowledge begins with these top free courses

Free mode

The Physics of Electronic Polymers (PEP)

Free mode

Energy to Electrochemistry Final Exam

Free mode

Electrochemistry

Free mode

Big Bang and the Origin of Chemical Elements

Free mode

Preparing for CLEP Chemistry: Part 1

Free mode

Pre-University Chemistry

Professional development for Educators

Your path to becoming a giant of knowledge begins with these top free courses

Free mode

BlendedX: Blended Learning with edX

Free mode

Teaching With Technology and Inquiry: An Open Course For Teachers

Free mode

Teach computing: Physical computing with Raspberry Pi and Python

Free mode

How to Learn Online

Test your knowledge

What is the relationship between atoms and light, and how can it be explained from physics?

Light can be understood both as an electromagnetic wave with defined frequency, wavelength, and energy, and as particles called photons that carry quantized energy. At the atomic level, light interacts with the electrons of atoms: when a photon with the right energy hits an atom, it can be absorbed by an electron, causing it to jump to a higher energy level; conversely, when an electron drops from a higher level to a lower one, it releases a photon with specific energy. This process of photon absorption and emission is fundamental for understanding spectral phenomena, color, and the behavior of light in atomic systems.

How does photon absorption and emission occur in an atom, and what are the consequences for the system’s energy?

When an electron absorbs the energy of a photon, its internal energy increases and it “jumps” to a higher level, called an excited state. This state is usually unstable, so after a short time, the electron returns to a lower level, releasing the extra energy as a new photon of light. Each transition between energy levels produces photons with specific energy, frequency, and wavelength, giving rise to the characteristic absorption and emission spectra of each element. This means that atoms “respond” to light individually, depending on their particular electronic structure.

How can we observe different colors in light spectra when electrons change energy levels?

When an atom emits a photon while returning to a lower energy level, the energy of the photon determines its frequency and wavelength, and therefore the color of the light. For example, if the energy difference between two levels is small, the photon has lower energy and the light may appear red; if the difference is larger, the photon has higher energy and the light may appear another color. This phenomenon explains why each element produces a unique emission spectrum, like a fingerprint, which can be used for experimental identification.

Does it make sense to think of light as both particle and wave when interacting with atoms?

Yes, this duality is one of the most fascinating aspects of light. Light behaves as an electromagnetic wave when propagating through space, with constant speed and properties like frequency and wavelength, but it also behaves as a particle (photon) when interacting with electrons in atoms, absorbing or emitting energy in discrete amounts. This dual nature of light is a fundamental principle of quantum mechanics and explains how light energy is exchanged in “packets” in atomic processes without any physical contradiction.

Why does visible light represent only a small part of the electromagnetic spectrum?

Visible light is only a fraction of the full electromagnetic spectrum, which ranges from low-energy radio waves to high-energy gamma rays. The portion we perceive as visible lies within certain wavelengths, approximately from violet to red, because our eyes evolved to detect these ranges. However, the same principles of photon absorption and emission apply to the entire spectrum: atoms and molecules interact with other forms of electromagnetic radiation outside the visible range, which has applications in chemistry, astronomy, and technology.