Area and Mesh Light

Area lights have many additional options. Most importantly, any geometry
can be selected to act as "geo light"

Light Spread

Specifies the spread of the light. A spread of 1 is to natural "cosine" spread. Lower spreads will produce a more focused light.  From left to right: 0.5, 0.2 and 1.0 (default).

Normalize Intensity by Area

Visible to Primary Rays

Makes area light visible to primary (a.k.a camera) rays. From left to right: off (default) and on.

Two Sided

When enabled, area light will illuminate from both sides. Note that this has no effect with the sphere shape. From left to right : 

Default Shape

Allows you to select the shape (left to right): square, sphere, disk and cylinder.

Select Geometry ...