Adding a texture to an area light can make it produce softer and more detailed highlights and an overall more organic lighting effect.
Since an Area light in Blender isn’t rendered as an actual mesh object with UV coordinates, it’s texture coordinates are parametric (see below).
Adding a texture to an Area Light:
In the Area Light properties click the Use Nodes button (see image A) to initiate its node graph and allow texturing it.
In the Shader Editor view (with the light selected), drop your texture to the light’s node graph and connect it to the light’s Emission node’s Color input. (see image B)
Create a new Input > Geometry node, and connect it’s Parametric output to the Image Texture’s Vector input. (see image B)
A. Without a texture the Area light produces a hard flat highlight:
B. With the vignette texture, the Area light now has a more subtle organic effect:
* The Emission node’s Strength was increased in this case to compensate for the lower light output with the texture. Related posts:
The most realistic way to create real world metal shaders is to use Complex Fresnel reflection. Cycles has a general implementation of a Complex Fresnel reflection in its Principled shader (when Metallic is set to 1.0), but this implementation doesn’t allow using real world physical numeric Complex IOR values in order to accurately render physical metals.
You can use a Complex IOR OSL shader such as this one from Chaos Group,
But there are some limitations with it:
1) It isn’t supported in GPU rendering.
2) For some reason I don’t know I couldn’t get it to work with Cycles..
The Cycles Tangent node defines a Tangent-Space for a mesh by either using one of the object’s local axes (see image A) or by using an available UV layout.
This can be useful when designing an Anisotropic reflection shader like in the case of brushed, machined or lathed metals.
A grey-scale texture can be connected to the Rotation input of the shader to define changes in the Anisotropic direction on the surface (see image B).
A. In this example the Tangent node is set to ‘Radial’ Direction mode, in which a object axis is chosen as the radial axis of the Anisotropic direction:
B. In this example a Noise texture’s Factor output is connected to the Anisotropic shader’s Rotation input to create an irregular Anisotropic (metal brushing finish) direction: