Emission Nodes

Mesh EmittersThe ability for a surface to emit illumination usually described by a Black Body or Texture emission type. allow an object to be used as a light source. This can be used with both Texture and Sun / Sky lighting systems.

In order to use a mesh as a light source, it needs to be changed to a Diffuse materialUsed for dull, non-reflecting materials or mesh emitters. type. The Emission parameter has two different options:

Blackbody: The Blackbody Emission type uses Colour Temperature (in Kelvin) and Power to control the colour and intensity of the light.
Texture Emission: This allows any valid texture type to set the light intensity. This can be used to create neat effects such as TV screens by using an Image Texture as the source.

Emission nodes have a Sampling Rate parameter to control how much weight is given to the emitter when picking an emitter to sample. This allows you to choose which light sources will receive more samples. The emission sampling rate can be set to 0, which means that the emitter will be excluded from the direct light calculation.

Blackbody Emission Node

The following settings are listed for the Blackbody emission settings, but many of the settings are shared with the Texture emission settings. The main difference is whether the colour comes from the Blackbody temperature or from the texture settings of the diffuse material.

Temperature – The temperature (in K) of the light emission.
Power – This is the wattage of the light source. Each light in the scene should be set to its real world wattage. For example, a desk lamp could be set to 25 watts, a ceiling lamp to 100 watts, and an LED light to 0.25 watts. This setting should not be used to balance the lighting power of the scene.
Efficiency or Texture – This setting is used to set the efficiency of the light source. No light is 100% efficient at delivering the power at the specified wattage (a 100-watt light bulb does not actually deliver 100 watts of light.) T he efficiency setting can be used to enter the real-world values. These values can be used to create very realistic light settings. For example, a standard 100 watt incandescent bulb would only be approximately 2.0% efficient where as a 25 watt compact fluorescent light will be 10% efficient. These will both produce around the same quantity of light in real life.
Orientation – This setting is used to adjust the direction the light is pointed in the scene. This setting only affects lights using a non-uniform distribution (textures or IESAn IES light is the lighting information representing the real-world lighting values for specific light fixtures. For more information, visit http://www.ies.org/lighting/. files).
Distribution – The distribution controls the pattern of the light. This can be set to a floattexture and an image or IES file can be loaded.
Cast illumination – Disabling this option will disable emission, i.e. it won’t be visible in diffuse reflections, but still be fully visible in specular reflections. It will also be excluded from the direct light calculation.
Surface brightness – Enabling this option will cause emitters to keep the surface brightness constant independent of the emitter surface area, i.e., the total emitted power will be dependent on the emitter surface area. The scaling is done in a way that a texture emitter will produce the same colour in the rendering (if the diffuse channel is black), when the camera response curve is set to “Linear/off”, exposure to 1, gamma to 2.2 and vignette to 0. Disabling the option will keep the total emission power constant — i.e., the surface brightness will become dependent on the emitter surface area.

Texture Emission Node

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