This attribute gives the appearance that the material is emitting incandescent light. Note that a Mesh Light may work better in a situation where you need an object to emit light that casts realistic ray-traced shadows.
Emission
Controls the amount of emitted light. It can create noise, especially if the source of indirect illumination is very small (e.g. light bulb geometry). Note that a mesh_light may work better in a situation where you need an object to emit light that casts realistic ray-traced shadows.
Bulb with emissive shader assigned to it (rollover image) Increasing the number of diffuse samples will help to reduce any noise in dark, indirectly lit areas of a scene when using emission.
Color
The emitted light color. Texture map representing hot lava connected to emission_color