Reflections. Fresnel effect.

Light reflects from objects. It is the way we see the world. In fact we see the light, not objects. Light which is not reflected, either absorbed or refracted. Intensity of reflections depends on type of surface. Mirror reflects 100% of light, because there is no light which absorbed or refracted. Sum of reflected, absorbed and refracted light is equal light, that falls on surface.

Few rules for reflections:
- Angle of falling of light ray is equal angle of reflection of light ray
- Reflected ray lays into one plane with fallen.
- The more angle of falling ray, the more intense this ray.



Author of last rule is Fresnel. In 3ds max this rule realized this way:


Or with help of fallof map


Lets use the next scene for the tests (box and sphere in glowing cylinder)


Notice that on the edges of sphere intensity of reflection is growing up. It is how Fresnel rule works. The more vivid examples in real life are reflection on cars, windows and puddles.


Diffuse reflection
Reflection in most cases not glossy, but diffuse. For example we can't see our reflection in asphalt. But can see it in a puddle easy. It depends on type of surface. Puddle is smooth, therefore reflect light in one direction and asphalt has a roughness, so reflect light in different directions.





In 3d it realized with parameter refl. Glossiness.


Reflections in 3d
Now let's stop more fully on that how reflections realized in 3d. I am using vray, but think that essence is same for different rendering engines.


Reflect
color responsible for reflection nature. Black color means no reflections and white - maximum reflections.

Reflection glossiness
1 glossy surface, 0 – matt.

Highlight. Glossiness
attached to refl.glossiness and responsible for glossiness of light sources reflections.

Subdivs
responsible for quality of reflections and, accordingly, for rendering speed

Fresnel reflections
activates Fresnel effect.

Fresnel IOR
It take part in Fresnel formula and responsible for how much Fresnel effect influences on reflections. When IOR equal 1 there is no reflection at all and when IOR is 100 reflection looks like there is no Fresnel effect.



Сonclusion
Almost all objects in our world has Fresnel effect. I advice to use it for achieving more realistic look for your materials. Every object has it's own IOR.
For 3d purposes the more suitable next values:
Water 1.333
Glass 1.33 - 1.5
Diamond 2.13
Wood, stone, concrete, etc. 3-4
Plastics 5-8
Metalls 20-100

Feel free to write any questions, wishes and remarks ;)