Lighting can make or break any 3D scene.  A beautifully modeled object, terrain or person will look terrible with improper lighting, but if lit properly, nearly anything will look realistic because the lighting will convince the viewer that the object or scene is real.  For simple materials, realistic lighting isn’t too difficult to achieve, however, with transparent or translucent materials, glossy materials, liquids and others, achieving realistic lighting can be a bit tougher.

The key to working with lighting for these types of materials is caustics.  Caustics is light rays being reflected or refracted through a material, creating a focused light ray on the other side of the material.  In this tutorial, you’ll learn how to achieve simple yet realistic caustics in 3D Studio Max.

If you have any questions, let us know in the comments and we’ll do our best to help you out.

Here is the final result we are looking for.

I will be using 3ds Max 2010 for this tutorial but you can use any earlier version.

What Is A Caustic ?

A caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light. In simpler words, a caustic is a bundle of light rays. For example a caustic effect may be seen when light refracts or reflects through some refractive or reflective material, to create a more focused, stronger light on the final location. Such amplification, especially of sunlight, can burn — hence the name. A common situation when caustics are visible is when some light points on glass. There is a shadow behind the glass, but also there is a stronger light spot.

The 3D Scene

For this tutorial, I basically created 3 Torus Knots but you can create any object you want. The Torus Knots are sitting on a plane with a curve towards the back for a seamless infinite background effect.

The Light

Now this is the important part. Create a mental ray spot light (mr Area Spot) and using the above image as refrence, arrange the spotlight in the scene. Also, turn on the Shadows and set it to Ray Traced Shadows. You will also notice that I have decreased the spot light’s Hotspot/Beam to really concentrate on just the geometry and made the Falloff/Field almost 4 times to have the spotlight gradually illuminate the surrounding plane.

The settings of the mental ray Spot Light are as below :

Note that the settings such as multiplier, hotspot/beam , falloff/field are scene dependent.

The Shaders

I will be using the Glass (lume) mental ray shader shipped with 3ds Max.

Bring up the Material Editor by Pressing “m” and click on the “Get Material” button in the material editor

.

From the Material/Map Browser, select mental ray

and click OK.

NOTE : Make sure you have set your renderer to mental ray in the Render Setup otherwise the mental ray shader won’t show up.

Now, in the mental ray shader setup, click on the empty slot next to “Surface” under Basic Shaders and from the Material / Map browser, select Glass (lume) and click OK. You can leave all the settings to their default values.

Come back to the mental ray shader setup and click on the empty slot next to “Photons” under Caustics and GI and from the Material / Map browser, select Photon Basic (base). Again, you can leave everything to default.

This is how the shader should look like after the setup.

Assign this shader to the model in your scene. I created an additional green colored shader and applied it to the smaller Torus Knots to show colored caustics.

Render Settings

Open the Render Setup panel by going to the Rendering Menu > Render Setup or by pressing F10. Go to the Indirect Illumination tab and under it enable Final Gather with default settings and also enable Caustics under Caustics and Global Illumination (GI).

For this scene I cranked the multiplier up to 100 instead of the default 1 to get the caustics to really show. The Maximum No. Photons Per Sample was kept at 50.  Also, I changed the Average Caustic Photons Per Light to 1000000 from the default value of 20000.

Render

When you click Render, mental ray will calculate the Photon Emission and the Final Gather which might take some time but after the image has been rendered, it should look something like this: