Advanced Lighting Techniques Part 2

by Montree T. (easyyong@hotmail.com) - Smoke3dStudio

5. Playing with light multipliers and shadow density

5.1. Negative multiplier parameter of light changes the light to be a shadow.

When we create a large scene some object's shadows may not appear correctly and some may be missed. A good way to create an accent shadow on an object is to place a light at the object's shadow position and change its multiplier to be negative.

Placing a negative omni behind the teapot the effect look like a shadow.

When the multiplier is negative, the color will be effected as well. For example, a green colored light will appear inverse (become dark red) when the multiplier parameter is negative and white colored light will become black after we change its parameter to be negative.

5.2. Playing with shadow density

Now we are playing with positve shadow density. The postitive density (more than 1) causes the shadow color to be come brighter (with the exception of a black color shadow, the positive density will make the shadow appears darker).

Sometimes when we want to create a lighting effect behind an object which has a complex shape (ie. text or free from object), the first way is to use many omis, placing them to follow the object's contour.

6. The second bounce and sub-ambient

The second important thing besides the ambient (that I've mention in Part 1 of this tutorial), that will make the scene look more interesting, is indirect illumination.

In the real world, there are many lights bouncing/scattering around. It's hard to imagine this and apply it to your own scenes started from scratch, unless you copy a photo or use a powerful GI plugin. We don't need to put all illumination in a scene. It's good enough if our eyes only capture a second or third bounce from the main light source ie. illumination from sunlight, illumination from a big light source and etc.

Placing omnis as a direct illumination from a diffuser.

Adding omnis to simulate 2nd light bounce makes the scene look more interesting. Around the 2nd bounce area is also a sub-ambient light in the scene. This means the objects around the omni attenuation will be affected by its color. From the picture above, notice the white chairs and ceiling affected by the light- blue light from the 2nd bounce.