What Is The Index Of Refraction (IOR) Of Glass?


IOR Of Glass
IOR Of Glass

Materials have a variety of properties to influence how the material is going to respond when hit by a source of light. These properties can include diffusing, refraction, and subsurface scattering depending on the material. A common question is finding the specific IOR value with a material like glass.

The index of refraction for glass ranges from as low as 1.44 to as high as 1.95, as glass is created in various ways to be used with different applications such as windows, glass bottles, and safety glass. Each type of glass has a different structure and therefore a different IOR value assigned to it.

So we have a rough idea of the values that we can use to acquire the correct behavior of a glass material but need to go into a bit more detail on what the actual values are for each of the different types of glass, and also why you should bother with the index of refraction in the first place.

IOR Values Of The Different Types Of Glass?

Note: We have conducted our own research into what the typical values are for commonly used types of glass, performing tests with glass objects in Blender itself and comparing them to real-world counterparts. We have also researched multiple sources as some sources suggest different values to others.

What we have found is that there is no exact value to a specific type of glass, but a very small range of values that can be used. This is because most glass is created using various components and temperatures to create the variety of glass objects used in everyday life. This process is not perfect and does not create identical results each time because of the variety of the composition in the glass.

Type Of GlassIndex Of Refraction
Window Glass1.51 – 1.52
Acrylic Glass1.49 – 1.492
Bottle1.51 – 1.52
Television1.49 – 1.51
Guerilla Glass1.50 – 1.51
Drinking Glass1.504 – 1.523
Headlights1.47 – 1.49
Flint Glass1.56 – 1.89
Glass Crown 1.517 – 1.52
Bulletproof1.49 – 1.50
IOR For Common Forms Of Glass

What Is Index Of Refraction?

We can’t describe what the index of refraction is without first explaining the process of refraction itself. Refraction is when light is redirected as a result of the light passing from one medium to another. For example, if you shine a beam of light from a torch at a diamond, the first medium is the air between the source and the object, while the second medium is the diamond itself.

When the light makes contact with the surface of the diamond, this is the moment it passes from one medium to the next. The light is redirected from this point as it travels through the object looking to pass through the other side. This is what we call the process of refraction.

So now that we know what refraction is, we can tell that the index of refraction is the amount of refraction that occurs when the light hits the surface of the object.

How is it measured?

Rather than starting from 0, the values for refraction use 1 as the starting value. A value of 1 is the same as there being no refraction at all. The light will pass through the object as if it was still passing through the air, with this we can also say that the index of refraction for air is 1.

Yes, gas can have an index of refraction, as all states of matter react to light. liquid can also have an index of refraction, for example, clear water has an IOR of 1.33.

The further away the IOR is from the base value of 1, the more the light beam refracts and changes direction. Considering how we know a diamond reacts to light in the real world, it will come as no surprise to learn that diamonds have a very high IOR value of 2.418.

The large majority of objects are found to have an IOR value between 1 and 2 but there are exceptions to this such as diamonds. Glass has a typical base value of around 1.50 but as we have seen can fluctuate in and around this value.

Why Do We Need The Correct Index Of Refraction?

Different materials will respond to light in different ways, and refraction plays a key role in how a transparent or translucent object will look as we can actually see the level of refraction taking place in the reflection of the glass itself. While not as important for rougher diffuse surfaces like wood, it is always needed to achieve true realism of a material to have the correct index of refraction.

What Are Some Of The Other Principles Of Glass Materials?

In addition to how much a beam of light refracts when it passes through the surface of the material, there are also other attributes we need to consider if we are looking to create a PBR quality material. Let’s briefly gloss over these attributes.

Reflection/Roughness

While refraction is the changing of direction for a beam of light that passes through an object, reflection is how the light bounces off and away from the surface. By manipulating the roughness value we can control how much light is reflected straight back and how much it is scattered. Most types of glass are very clear and so have a very low roughness level.

Fresnal

While all objects possess the property of reflection the amount of reflection is not always constant across the whole surface when viewing the object. The fresnel principle implies that an object’s surface appears more reflective to the human eye when viewed from an angle compared to viewing it straight on. For example, the surface of a body of water can reflect its environment when viewed from an obtuse angle.

Coloration

In Blender, you may notice that your glass material appears darker than you would expect, but this is in fact correct behavior for glass. The darkening is an effect caused by the refraction itself and is stronger in glass objects that have greater thickness.

Transparency

A fairly obvious one, it is the effect of being able to see through the surface of an object. The principled glass shader will do this by default in Blender. The only exception for glass is when the roughness is increased to create a frost effect.

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