Understanding the Fresnel Effect
The Fresnel Effect is one of my favorite light effects.
When I’m painting a reflective surface, “adding Fresnel” is my go-to solution. It’s a tiny tweak with a big impact.
Look at the image below and notice how the brightness of the tabletop changes.
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.
The principle of the Fresnel effect is simple:
Steep angle = weak reflection, shallow angle = strong reflection.
I was blind to the Fresnel Effect 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: reflections change across distance – because the angle of incidence changes. As you look down to the ground close to your feet, the angle of incidence 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:
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.
On curved surfaces, the angle of incidence gets steeper towards the edges of the form. On a cylinder, the fresnel effect leads to the specular reflections being most visible in the red areas:
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 might enjoy learning about the 11 Modeling Factors – light effects that create the sensation of form.
PPS. Here is a nice example of the Fresnel Effect in a 3D program.