Fluorescence
Fluorescence - from XRF to Halloween costumes, is based on the same principle - the photoelectric effect. An electron absorbs enough energy from a photon to escape its orbital within an atom. However, electrons are in atoms for a reason, and an electron from another orbital quickly replaces the original. That moment of change - one electron shifting orbitals - releases the excess energy during the process. That excess energy - in the form of a photon, is what we see as the colors red, green, and blue.
Step 1: A light source
For the photoelectric effect to take place, we need a photon to come from somewhere. For most colors on Earth through its history, that has always been the sun. While traditionally expressed in terms of wavelength, this light can equally validly be expressed as energies. Blue, at 400 nanometers (nm), is also ~3 eV. Red, at 700 nm, is ~1.7 eV. Each color encodes a discrete energy. This isn't just true of visible light - energies below red are more commonly known as infrared, while energies higher than violet are called ultraviolet.
You'll notice there are many valleys in this spectrum - shouldn't it be smooth? In a vacuum yes but on Earth we have an atmosphere the light has to get through. Each valley represents absorption by a molecule - most reflect water, particularly in the IR range, though other molecules such as CO2 leave their marks as well. Humans have interrupted this pattern by introducing
Fluorescence - from XRF to Halloween costumes, is based on the same principle - the photoelectric effect. An electron absorbs enough energy from a photon to escape its orbital within an atom. However, electrons are in atoms for a reason, and an electron from another orbital quickly replaces the original. That moment of change - one electron shifting orbitals - releases the excess energy during the process. That excess energy - in the form of a photon, is what we see as the colors red, green, and blue.
Step 1: A light source
For the photoelectric effect to take place, we need a photon to come from somewhere. For most colors on Earth through its history, that has always been the sun. While traditionally expressed in terms of wavelength, this light can equally validly be expressed as energies. Blue, at 400 nanometers (nm), is also ~3 eV. Red, at 700 nm, is ~1.7 eV. Each color encodes a discrete energy. This isn't just true of visible light - energies below red are more commonly known as infrared, while energies higher than violet are called ultraviolet.
You'll notice there are many valleys in this spectrum - shouldn't it be smooth? In a vacuum yes but on Earth we have an atmosphere the light has to get through. Each valley represents absorption by a molecule - most reflect water, particularly in the IR range, though other molecules such as CO2 leave their marks as well. Humans have interrupted this pattern by introducing