<p>@PaulHK explained it very well in the comment section:</p>

<blockquote>
  <p>Ambient is a (rough) approximation of indirect lighting. For example, an outdoor object would be lit by the sun but the surfaces facing away from sun would be black if using only lambert shading, we can use dark gray for the ambient colour to mimic the effect of indirect lighting from the ground and sky</p>
</blockquote>

<p>If you were to visualize this with a shading model, say Phong, the Ka, Kd and Ks values would correspond to the following lighting calculations.</p>

<p><img src="https://i.sstatic.net/n5SA0.png" alt=""></p>

CC BY-SA 4.0
2018-07-12T04:32:32.467Z
2018-07-12T04:32:32.467Z
Varaquilex
<p>I am reading this <a href="http://paulbourke.net/dataformats/mtl/" rel="nofollow noreferrer">piece of documentation</a> to understand mtl files</p>

<p>So far I am stuck trying to understand the difference between ambient, diffuse and specular reflectivity (Ka, Kd, Ks).</p>

<p>If I am correct specular is "straight line" reflectivity (the kind of reflectivity of mirors), diffuse is the reflectivity of scattered light (the kind of reflectivity of many rough plastics). But then what is ambient reflectivity?</p>

CC BY-SA 4.0
2018-07-12T02:41:55.637Z
Ambient is a (rough) approximation of indirect lighting. For example, an outdoor object would be lit by the sun but the surfaces facing away from sun would be black if using only lambert shading, we can use dark gray for the ambient colour to mimic the effect of indirect lighting from the ground and sky.
PaulHK
<rendering><color><global-illumination><reflection><material>
Understanding material .mtl files
Makogan
# Understanding material .mtl files

(Asked by: username_0 on 2018-07-11)

I am reading this [piece of documentation](http://paulbourke.net/dataformats/mtl/) to understand mtl files

So far I am stuck trying to understand the difference between ambient, diffuse and specular reflectivity (Ka, Kd, Ks).

If I am correct specular is "straight line" reflectivity (the kind of reflectivity of mirors), diffuse is the reflectivity of scattered light (the kind of reflectivity of many rough plastics). But then what is ambient reflectivity?

**Tags:** rendering, color, global-illumination, reflection, material

> **Comments:**
> **username_1**: Ambient is a (rough) approximation of indirect lighting. For example, an outdoor object would be lit by the sun but the surfaces facing away from sun would be black if using only lambert shading, we can use dark gray for the ambient colour to mimic the effect of indirect lighting from the ground and sky.  

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## 1 answers

### Answer by username_2 on 2018-07-12. Score: 1 | Accepted answer

@username_1 explained it very well in the comment section:

> Ambient is a (rough) approximation of indirect lighting. For example, an outdoor object would be lit by the sun but the surfaces facing away from sun would be black if using only lambert shading, we can use dark gray for the ambient colour to mimic the effect of indirect lighting from the ground and sky

If you were to visualize this with a shading model, say Phong, the Ka, Kd and Ks values would correspond to the following lighting calculations.

![](https://i.sstatic.net/n5SA0.png)


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