The Fresnel Effect

The Fresnel Effect is one of my favorite light effects.

“Adding Fresnel” is one of the first things I do when I’m working on making reflective surfaces more believable.
It’s a tiny tweak with a big impact.

Watch the gif below and notice how the brightness of the table top changes.

fresnel effect example animation

How does it work?

To understand the Fresnel Effect, you have to understand the basics of reflections.
We’ll keep this minimal – the key is the Angle of Incidence.
The Angle of Incidence is the angle between your line of sight and the surface of the object you are looking at.

fresnel effect - angle of incidence

The principle of the Fresnel effect is simple:
Steep angle = weak reflection, shallow angle = strong reflection.

fresnel effect - angle of incidence examplesAnother Example

The Fresnel Effect is one of those things I was blind to until someone pointed it out to me — now I can see that it is everywhere! If you’re looking for it, you’ll find it.

Here is another example of how reflections change across distance – because the angle of incidence changes. As you look down to the ground close to your feet, the angle is very steep. If you look at a point on the ground that’s further away from you, the angle gets more shallow – and the reflection becomes more visible.

Here is the breakdown:

fresnel effect - angle of incidence illustration

And here is what we see from the viewpoint of the person. Use the arrows to the left and right of the image below to switch between versions with Fresnel Effect and without Fresnel Effect.

Look Around You

Take a look around the space you are in. Can you find an example of the Fresnel Effect? Look at shiny floors and plastic surfaces. Crouch down as I did and see how the intensity of the reflection changes.

To learn more, here is the Wikipedia article on Fresnel Equations.

Happy hunting! 🙂

PS. If you find this interesting, you’ll probably enjoy learning about the 11 Modeling Factors – light effects that create the sensation of form.

4 thoughts on “The Fresnel Effect”

  1. Kevin
     ·  Reply

    I’m trying to get this effect to work as part of a Computer Graphics project..

    The angle they actually care about when calculating the amount of reflected light (and possibly refracted light, for transparent objects) is between the vector (or ray , if you prefer) created from the viewer to the spot you’re looking at on the object, and the surface normal of the object.

    In other words, if you look directly down at the table, the angle is close to zero, and as you get closer to eye level with the table, the angle increases. This makes it easier to explain that “as the angle increases, the amount of reflection increases.”

    • Dorian
       ·  Reply

      Thank you Kevin!
      I wanted to use as few technical terms as possible in order to keep the article short and easy to understand.
      The surface normal is a very useful concept and I like your way of using it to describe the principle behind the Fresnel Effect.

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