There are times in which we want to have specular highlights without the diffuse lighting. We can create a Specular Highlight only light with a light Gel. This will greatly reduce rendering time compared to a full specular and diffuse light.
Let us start with a simple scene, a crystal ball.
The starting crystal ball
We want to play a bit with the specular highlights and the caustics, without adding too much light to the scene.
The solution is creating a Light gel that eliminates the diffuse lights and maintains the specular highlights.
The Gel with a Diffuse Reflectance of zero
This gel, applied to point lights will enable us to add a lot of speculars and caustics without washing the scene out.
Several lights. All but one have the gel applied
Render with gel. Notice the caustics and specular highlights in the ball
Same scene with no Image Gel for the lights. Render time was almost double, too.
Hope you find this technique useful.
