From BlenderWiki

Spot

Mode: All modes

Panel: Lamp (Shading context, Lamp sub-context, F5)

Description

Spot lamp.

A Spot lamp emits a cone shaped beam of light from the tip of the cone, in a given direction.

The Spot light is the most complex of the light objects and indeed, for a long time, among the most used thanks to the fact that it was the only one able to cast shadows. Today, with the integration of a ray tracer within the internal render engine of Blender, all lamps can cast shadows (except Hemi). Even so, Spot lamps’ shadow buffers are much faster to render than raytraced shadows, especially when blurred/softened, and spot lamps also provide other functionality such as “volumetric” halos.

Options

Lamp panel.

Common options: The Dist, Energy and Color settings are common to most types of lamps, and are described here.; The Layer, Negative, No Diffuse and No Specular settings control what the lamp affect, as described in this page.

Spotlight with Dist value of '20.0.

Spotlight with Dist value of 10.0.

Changing the Dist field value when using a Spot light also changes the appearance of the spotlight as displayed in the 3D Viewport:

Light attenuation drop-down list and Sphere button: These settings control how the light of the Spot decays with the distance. See this page for details.

“Shadow and Spot” Panel

When a Spot lamp is selected the following default layout for the Shadow and Spot panel is shown:

Without shadow.	With raytraced shadows.	With buffered shadows.
The Shadow and Spot panel when Spot lamp lighting is selected.

Options

SpotSi settings at 45.0 and 20.0 degrees.

SpotSi: The SpotSi (for “SpotSize”) slider controls the size of the outer cone of a Spot, which largely controls the circular area a Spot light covers. This slider controls in fact the angle at the top of the lighting cone, and can be between 1.0° et 180.0°.

SpotBL: SpotBL (for “SpotBLur”) slider controls the inner cone of the Spot. The SpotBL value can be between 0.0 and 1.0. The value is proportional and represents that amount of space that the inner cone should occupy inside the outer cone (SpotSi).

3D View of Spot lamp with a SpotBL setting of 0.5.

Render of Spot lamp with a SpotBL setting of 0.5.

The inner cone boundary line indicates the point at which light from the Spot will start to blur/soften, before this point its light will mostly be full strength. The larger the value of the SpotBL the more blurred/soft the edges of the spotlight will be, and the smaller the inner cones circular area will be (as it starts to blur/soften earlier).

To make the Spot have a sharper falloff rate and therefore less blurred/soft edges, decrease the value of SpotBL. Setting SpotBL to 0.0 results in very sharp spotlight edges, without any transition between light and shadow.

The falloff rate of the Spot lamp light is a ratio between the SpotBL and SpotSi values, the larger the circular gap between the two, the more gradual the light fades between SpotBL and SpotSi.

SpotBL and SpotSi only control the Spot light cone’s aperture and softness (“radial” falloff), they do not control the shadow’s softness as shown below.

Render showing the soft edge spotlighted area and the sharp/hard object shadow.

Notice in the picture above that the object’s shadow is sharp as a result of the raytracing, whereas the spotlight edges are soft. If you want other items to cast soft shadows within the Spot area, you will need to alter other shadow settings.

Spotlight with a Square light area.

Square: The Square button makes a Spot light cast a square light area, rather than the default circular one.

Shadows and Halos

The other options in this panel are about shadows and volumetric effects. The Spot light source supports raytraced and buffered shadows, along with halos, follow these links for in-depth descriptions of these topics.