Tutorial 1: Selective Lighting

Gaffer's selective lighting options are a powerful feature that allow you to exclude, boost, or dim the effect of lights on a given surface, or even use a negative value to suck light away from the surface. It also allows extra control of the way light falls off with distance.

In this tutorial, we will be lighting an urn object (supplied in the tutorials file) so that we can build various metallic surfaces using the anisotropy and specular features in the next few tutorials. Go ahead and load "sl_urn.lws" into Layout and render frame 0 to see what we have to work with. It's not a very exciting object or surface, but we'll work on shaping this into something much nicer.

If you look in the "lights" panel, you will notice that we have four lights. "Main" is a spot while the remaining lights (fills) are points, all of which are set to 100% light intensity. We also have the default 25% ambient light intensity which is way too bright, so set it to 0%.

Our first step is to isolate the fill lights so they only fall onto the urn. This lets us tweak the urn lighting without having odd highlights also hit the ground. We'll do this by using Gaffer on the ground to tell the ground not to "see" these fill lights.

Open LightWave's "Surfaces" panel, apply Gaffer to the "ground" surface, and go into Gaffer's options. Under "Light Intensity Adjustments" type "Fill" under "Prefix" (Note: This is case sensitive) and set a "boost" value of 0%. This identifies the lights we want to control (those that start with the letters "Fill"), and what we want to do (set their intensity for this surface to 0%). This effectively makes the the fill lights behave as if they were at 0% intensity (none!) only for the ground object, leaving only the spotlight still illuminating the ground. Notice how the number to the right of the row changes to "3" to show that these controls are affecting three lights.

If we had not named our three points with a prefix of "Fill" we would've had to name each one in Gaffer's prefix field. This would not be that big of a problem with only four lights and two surfaces. But what if we had a dozen lights and 20 or more surfaces? In that case, careful naming of the lights would still allow good control of the different sets. A good rule of thumb is to descriptively name your lights in a way that you can easily group or define them in Gaffer. One good method is to name them based on both type and position, like Fill_front, Fill_left, etc. This allows you to group or define all of the "fills" while having the flexibility to single out a certain "Fill" for further adjustments by tweaking it in Layout's Lights panel.

Render a frame to see how our scene looks. The urn is unchanged, but the ground shows only the effect of the single spotlight, as we planned. The final lighting adjustments are to the urn's surface. We want to have all of the lights affect the urn, but the fills are a bit bright. We could simply dim all of the fill lights in LightWave's light panel, but let's use Gaffer instead to demonstrate how lights can be dimmed for a single surface.

Apply Gaffer to the urn surface and go into Gaffer's options. Once again type "Fill" into the "Light Intensity Adjustments" "Prefix" field, but this time enter a value of 50% for "Boost." This halves the intensity of the Fill's on the urn's surface.

Also, set the "Primary Specularity" value to 0%. This turns off specularity for the urn, which gives us a starting point for the next tutorial. We could do this in LW's surface panel, but sometimes it's just more convenient to do it in Gaffer since you're there anyway.