In the older days of rendering the mention of specular highlights would bring to mind shiny little round white dots on the typical render sphere. The importance in this classic specular is that it meant to represent reflected light, and the reflection attribute would be environment reflection and other objects in the scene. These days with advanced rendering packages the specular reflection attribute can get its meaning confused.
In a truer definition, specular reflection is the ‘perfect’ mirror like reflection due to the incoming light rays being reflected at the same incidence angles:
To confuse matters more with specular reflection, newer render engines tend for specular reflections to mean “blurry reflection”. An artist then can blend between using specular (“blurry”) reflection model along with pure reflection (like classic specular above) or by itself. These new specular rendering models are raytracing and actually perform reflection raytracing.
In contrast, diffuse reflection is to be simply put the colour we see reflected back to our eyes because the light reflected gets scattered about.
What this means to Cinema 4D
With plugin renders for Cinema 4D like Vray and Mental Ray the new specular reflection rendering will actually allow an artist to create speculars that model the light shape and where blurry reflection options are used the environment can also be reflected in the blurry reflection. The reflection channel in these renderers are then usually reserved for “mirror” reflections and thus the confusion is evident in our terms of specular vs reflection.
Getting back to Cinema 4D, when we use the specular channel it will treat our light sources as a point source and therefore we render a white dot (because we are assuming classic white specular without changing other settings). Try lighting a simple sphere with a rectangular area light and we see that familiar circular dot; this is just not true to form because our light source is a rectangle.
We can solve this by using the Lumas Shader. I will cover this example in a few simple explanations and leave the help documentation reading to you for more detail. Suffice to say the Lumas Shader seems to provide some raytracing function to reflect our light source shape in the specular. Keep in mind this is not a mirror reflection but rather simulating what we simulate in other renderers with blurry reflections.
It bears mentioning that the Lumas Shader is what we can use to simulate multiple speculars in a material. When using the Lumas Shader for specular reflection be sure to deactivate the shader (Shader Properties) and use only specular channels and if desired Anisotropy.
The images below show the transition from using a specular channel and Lumas Shader for specular. You will need to be aware that in doing so we have to increase the samples of the area light to generate the shape which can/will increase render times.
And the lastly, mixing in some reflection to get the true raytraced reflections and allowing the light source to be seen in render we can compliment with Lumas to give our reflection a bit of bloom:
Specular is the light source reflection and Reflection is the object and environment reflections within the scene. Don’t be afraid to mix and compliment. Have a look at the material and see how light reflects upon it and consider that using a low grade specular can also “brighten” the material since we add specular to the diffuse and thus we can create a “sheen”.