9 Causes Of Interference Of Light:Detailed Facts

In this article, we are going to discuss various causes of interference of light with detailed facts.

When two rays of light superimposed on each other disperse their energies to one another are called the interference of light. Lets us see the following causes of interference of light in detail:-

Waves of Light are in the Same Plane

Whether in phase or out of phase, the two waves will interfere if they propagate in the same plane.

If the waves are traveling in a different plane such that no two waves intersect or move parallel to each other, then there will be no chances of getting the interference pattern.

Superimposition of Waves

The two waves are said to be superimposed if the two waves running in the same plane overlap while propagating in the same direction.

Superimposition of waves

If the crest and trough of one wave overlap exactly on the crest and trough of another wave respectively, then it enhances bright fringes and is called constructive interference. If the crest and trough of the first wave fall on the trough and crest of a second wave, then it will produce dark fringes. This type of interference that cancels out the crest and trough scraping the wave propagation is called destructive interference.

Read more on 4+ Types Of Interference Of Light:Detailed Facts.

Coherent Sources of light

If the phase difference between the two waves emitted from different sources having similar frequency and wavelength remains the same, then the two sources are said to be coherent sources.

This is an essential condition that causes interference of light. It helps to produce stationary waves by keeping fixed phase differences. Light waves must have constant wavelength and phase, the frequency of the light sources must be equal or similar to each other.

causes of interference of light
Candle Light;
Image Credit: Pixabay

It would be inadequate to use the sources of two different frequencies to get the interference pattern, if so; we would have seen abrupt changes in the phase difference. Due to this, the intensity of the light will change unexpectedly and no interference pattern will be observed.

Hence, the sources must be coherent to get stationary waves having constant phase differences and to sustain the constant intensity of the light.

Read more on 4+ Wave Interference Examples: Detailed Facts.

Wavelength of Light Equals the Dimensions of the Object

A light wave diffracting from the object at different angles interferes giving vibrant colors of light.

causes of interference of light
Soap Bubble;
Image Credit: Pixabay

You must have observed the light reflected from bubbles, thin film of oil, oily surfaces, pools, etc. The light ray incident on the thin layer reflects a part of the light from the top surface of the thin film, and the remaining is refracted through and gets reflect from the bottom layer of the thin film while a part of the light may be transmitted.

These reflected rays of light, reflect at different angles because on refraction the angle of refraction in the medium of thin-film differs due to the refractive index. Hence, the rays of light bend at different reflected angles due to which the rays of light interfere. On interfering with the light rays colorful patterns of light are formed on the objects.

Read more on Thin Film Interference Notes: Equation, Working, Dependence, Applications, Problems, and FAQs.

Energy of the Photons is Conserved

The conservation of energy by the photon of light is also an important factor for the interference of light.

If the energy of the wave is not conserved then the wave would have vanished after traveling to a certain distance and no interference pattern would be seen. The energy associated with the photon is given by the equation,


Where θ is a frequency of the light wave.

Since the energy is conserved, the above equation implies that the frequency of the light has to be conserved. If the light wave from the same source coincides with each other then we get the interference pattern of the light.

Narrow Sources of Light

If the sources of light are broad then the light rays emitting from different points would interfere among themselves would result in the overlapping of the interference of fringes and hinder the effect.

Light transmitting from narrow slit;
Image Credit: Pixabay

Hence, the monochromatic sources must be narrow.

Read more on 7+ Interference Of Light Examples: Detailed Facts.

Monochromatic Light

A monochromatic light source emits a light wave producing a unique wavelength and frequency. This will produce constructive interference of light.

If two different wavelengths of light are used then the destructive interference will occur at a certain point in between interference of waves giving dark fringes.

The Intensity of the two Monochromatic Lights is the Same

Monochromatic light means the source of the light that produces waves of light of constant wavelength. Two waves of similar frequencies and wavelengths interfere to give the interference pattern.

Sodium Light;
Image Credit: Pixabay

Since the wavelength and frequency of the wave are constant, this implies that the amplitude of the wave that is directly proportional to the intensity of the light wave is constant.

The light waves interfering with each other are of the same amplitude hence the resultant fringes produced on the screen due to interference of the two waves are of equal intensities.

Read more on 5+ Constructive Interference Examples: Detailed Facts.

Distance from Source and Screen is Large

The width of the fringes formed due to interference is directly dependent on the distance between the source and the screen where the two beams of light show interference patterns. If the distance is large then the fringes are broadly spaced.

If the distance is shortened between the source and the screen, then we may not get that broad view of the interference pattern that we can get at a bigger distance. If we held the screen near few centimeters away from the source then it is evident that we shall not get any interference of light.

Distance between Coherent Sources is Small

The fringe width is inversely proportional to the distance of separation of two coherent sources of light. It is given by the equation


Where x is a fringe width

D is a distance between source and screen

d is a distance between two sources

λ is a wavelength of a monochromatic light

If the distance between the two monochromatic lights is smaller then, they would easily interfere with one another. The fringes thus formed are broadly spaced are nicely visible.

Read more on 3+ Destructive Interference of Light Example: Detailed Facts.

Frequently Asked Questions

What is thin-film interference?

The wavelength of light penetrating through a thin film is equal to the dimension of the thin layer for the interference of light to occur.

The reflection of light from two layers of a thin film of solid or liquid interfere with each other to give a colorful pattern of light hence it is called thin-film interference.

How does interference of light take place?

For light waves to interfere, two or more waves of light has to be superimposed on each other.

When two monochromatic light waves of stable phase, and constant wavelength and the frequency overlap with each other, the interference of light takes place.

Define the term quantum interference?

The word quanta describe the discrete quantity of charged particle associated with mass and energy.

Quantum interference is the interference of the wave functions of the particle present in two different situations at a time in a wave.

What is constructive interference of light?

Two light waves of equal phase and equal frequency and amplitude interfere with each other; we get constructive interference of light.

The crest and trough of both the waves overlap on each other amplifying the effect such that the resultant wave produced gives the bright fringes as the amplitude of the wave increases.

What is destructive interference of light?

The phase difference between the two waves giving destructive interference is π/2.

The overlapping of waves having a phase difference cancels out with each other, giving no amplitude of the wave, resulting in zero intensity of light.


Hi, I’m Akshita Mapari. I have done M.Sc. in Physics. I have worked on projects like Numerical modeling of winds and waves during cyclone, Physics of toys and mechanized thrill machines in amusement park based on Classical Mechanics. I have pursued a course on Arduino and have accomplished some mini projects on Arduino UNO. I always like to explore new zones in the field of science. I personally believe that learning is more enthusiastic when learnt with creativity. Apart from this, I like to read, travel, strumming on guitar, identifying rocks and strata, photography and playing chess. Connect me on LinkedIn - linkedin.com/in/akshita-mapari-b38a68122

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