We all know that light is a form of energy that stimulates sight and makes things visible. But light shows many more properties that make us curious to learn more about it; One of those topics is the Energy of Light. Light behaves as particles (photons) and waves; Light shows us two natures, one is a wave, and the other is a particle; the concept of energy is mainly associated with the particle nature of light.
We know that light is a source of energy, but how? what kind of energy does light have? where does light store its energy? And Energy of the Light; we are going to answer all these questions in brief.

Light as Wave

The theory that all light behaves as waves in which electric and magnetic fields travel together at velocity c has been remarkably successful in describing many phenomena, such as reflection and refraction of light at interfaces between different media, interference effects resulting from wave superposition, and diffraction effects due to obstacles within the path of a light wave.

We describe light in terms of its electromagnetic spectrum, which includes ultraviolet (UV), visible (VIS or VISIBLE), infrared (IR), microwave and radio waves, X-rays, and gamma rays radiation. The light spectrum is the arrangement of colors in the order of their wavelengths, ranging from violet (380 nm) to red (760 nm) in nanometers. Different colors in the visible spectrum have different wavelengths and frequencies. Red color has a longer wavelength than green or blue. This is why the sun appears red at sunset or sunrise. Colors are additive, meaning when you mix primary colors, you get white light; when you combine secondary colors, you get complementary colors.

Light Spectrum

Some important terms

The speed of Light

3 X 10^8 m/s is the maximum speed at which energy or information can travel.

Frequency

It is the measure of the number of waves that pass a given point per second.

Wavelength

l is the distance between two successive crests or troughs of a wave.

Wavelength and frequency interrelation

Wavelength and frequency of Light are interrelated, l ν = c, where c is the velocity of light in a vacuum. The various colors we see are not due to different hues of light but due to reflection or absorption. Electromagnetic waves transmit radiant energy, the most familiar example being visible light.

Light as a particle

Gives us a clue about Energy of the light

Photon is the primary particle of light. Energy and momentum are related to Light by Planck's relation. Light is made up of photons, which carry energy that can be measured. The energy of photons directly depends on the frequency and inversely depends on wavelength.

Light shows wave as well as particle nature; this particle nature of light can be seen in the photoelectric effect that was proposed by Albert Einstein, for which he got the Nobel prize in 1921. Einstien gave the equation to calculate the energy of the light.

The photoelectric effect

The photoelectric effect is a phenomenon in which electrons are emitted from matter, typically a metal, when light shines on the surface.

How the photoelectric effect works

First, let's start with a basic definition of work function. Work function is the minimum energy (in electron volts) required to remove an electron from a metal surface. Light shining on the metal has energy in its photons. When the photon energy is greater than the work function of the metal, electrons can be emitted from the surface of the metal. This effect is called the photoelectric effect. Light having a given frequency f can emit an electron only if its energy hf exceeds the work function (or minimum kinetic energy) required for electron emission from that metal.

The magnitude of the cutoff frequency is smaller than or equal to the work function. The photoelectric effect is only observed if the frequency of light exceeds a threshold frequency, called the threshold frequency, which is characteristic of a particular metal. One of many famous experiments designed and executed by Einstein was to observe this effect for various metals and light frequencies. His observations allowed him to determine that light energy was quantized and that one quantum of light energy was equal to one hf (E=hf).

Einstein came up with a new theory of light called the photon theory of light. It is said that light is transmitted as single "particles," or quanta of energy, each quantum having an energy E = hf, where h = Planck's constant and f = frequency. This would eventually lead to a complete change in how we think about light.

The results of these observations were not consistent with classical physics. Still, they were when explained using Maxwell's electromagnetic theory of light in combination with Planck's hypothesis that electromagnetic radiation could only be released or absorbed in discrete packets (or "quanta").

When a photon hits the electron, it transfers energy to the electron and, by gaining the energy electron, tries to run out of the energy level of an atom; this behavior of the electron leads us to the creation of a spectrometer we will talk about this in our future blogs.

Conclusion:

Now, we know how light has energy in small packets of quanta; the energy of light depends on wavelength and frequency, and how Light transfers its energy to the electron which can be seen in the photoelectric effect; we know light as a source of energy, but now we know Energy of the Light.