The properties of a positional light (also called a omni or a point light) that we set here are color and position. We are using the color to illuminate the diffuse component of a material. For our example, the color is yellow at 50% saturation. We could use an omni light for specular reflection but we are using a spot light to illustrate that material property. The alpha value of the color becomes important only when alpha blending is enabled. Otherwise, it does not matter what alpha value is used.

The position is given as homogenous coordinates. When the fourth component is nonzero, the first three values are the x, y and z coordinates of the position. The current viewing transformation that is applied to the geometry is also applied to the position when the illumination calculations are carried out. Therefore, we give the position of the light in world (modeling) coordinates versus eye coordinates.