General Light Parameters
In addition to a light’s shape and the way in which it casts light, numerous other options and parameters are available, which are common to all light sources. Among these are the Color and Intensity of the emitted light in its General tab. Lights can also be assigned a material, which lets them be used as a slide or film projector. If a material whose Transparency channel contains an image or shader is applied to a light, the colors from this image or shader will be applied to the emitted light. An example of such an effect is shown in the image below in which an Area light projects a Gradient onto elements in the scene.
When using the light types Spot or Area, the Projection Flat is best-suited for precisely matching the size and angle of the texture to the direction in which the light is emitted. When using the light type Omni a Spherical projection type should be used.
The Use Temperature setting, which lets you define a color for a light source can also be selected. This parameter can be accessed by clicking on the small black triangle next to the color.
The Light Source’s Illumination
At first thought it might seem unnecessary to create a light source that does not cast shadows or even emit light. Don’t forget that lights are also used to create visual effects, e.g., as a flickering star in the night sky or for creating lens reflections. Several options are available in the General tab that can be used to have a light source work only as a Specular or to brighten the light’s Diffuse. For example, a light source can be used to create a specular highlght on an eyeball. You can also define whether or not a light is reflected from other surfaces when using GI Illumination.