Reason Behind Diffraction (Explained with examples)

We have learnt many interesting phenomena of science and diffraction is one of them but one question comes in our mind that what causes diffraction? or what is the reason behind diffraction? I'm going to reveal the answer to your question in this blog so stay tuned.

Diffraction is caused by the Huygens principle, according to this every point of lightwave acts as a source. When light waves can not pass through due to some obstacles, light bends at the ends of an obstacle. If there is a slit or hole in the obstacle light wave pass through it and this is called diffraction. 

Reason behind diffraction:

So let's understand about diffraction first before getting into what causes diffraction and the reason behind diffraction.

What is diffraction ?

When light waves encounter obstacles, light bends at the edges of obstacles or when light wave spreads after passing through a small opening of an obstacle then it's called diffraction.

Some of the examples of rainbow reflection on your CD or DVD, red appearance of the sun during sunset or sunrise. Well if you want to have a good idea of diffraction, I have an article on my site where different examples of diffraction are discussed in brief. Click on examples of diffraction to read that article.

What causes diffraction ? (Reason):

Huygens principle is the reason behind diffraction. According to Huygens principle, every point in a  light wave behaves like a source of light.

So, when light is encountered by any obstacle in its path, the light wave passes through a small opening or gap in the obstacles and spreads because each particle of lightwave behaves like a source.

What if there are no gaps or opening in the obstacle ?

If there is no gap present in the obstacle, still light passes through its edges and light bends and all these effects are what we call as diffraction. 

It will be better if you understand this with some examples. You can read our whole dedicated article on different examples and application of diffraction on our site. Click on examples of diffraction to read that too as well.

So now let's understand the reason of diffraction through some of the examples of diffraction and see where Huygen's principle is working in each of them.

Explained Examples of diffraction:

So let's start with some examples and try to understand how Huygen's principle takes place in each of these examples.

1. The light coming from the cloud:

You may have seen beautiful pictures formed by the cloud when light from behind the clouds can be seen which is also known as silver lining. Just like one in this picture but well, you know that it's also an example of diffraction because light bends around the corners of cloud and here in this case cloud is acting as an obstacle in the light path.

 Light coming from the back of a cloud
Light coming from the back of a cloud

Here when light waves encounter cloud, light bends at the edges of the cloud and we can see this beautiful scenery.

Here light spreads again after bending because according to Huygen's principle each particle from lightwave behaves like a source of light and that's why it spreads again just like a wave.

2. Bending of light at the corner of a door:

Bending of light at the corners of the door
So when the door of the darkroom is opened slightly, then you will notice that light enters our room from another room. Same as shown in the picture above. Well, in this case, the closed-door acts as an obstacle and still, you will notice that light bends at the edges of the door. This is also the example of diffraction.

Here also light bends at the edges after encountering an obstacle. When light bends it still spreads because of the Huygen's principle.


Diffraction is a phenomenon in which light still travels and spreads its path after encountering of an obstacle. Light passes through a small opening or if it's not able to find an opening it will bend at the edges of obstacle and spread.

The reason behind diffraction is the Huygen's principle according to which a particle of lightwave acts like a source of light so even after encountering of obstacle light passes through a small opening and spreads as every particle of a light wave is a source of light so it spreads in all direction.

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