The Black BodyAn opaque object that emits thermal radiation. In Octane, this is used to designate illumination properties for mesh emitters. emission map lets materials emit light. Emission maps work with the DiffuseAmount of diffusion, or the reflection of light photons at different angles from an uneven or granular surface. Used for dull, non-reflecting materials or mesh emitters. material type and connect to the Emission slot. There are two type of emission maps: the Black Body (figure 1) emission, and the Texture emission map.
Figure 1: The Black Body emission node connected to a Diffuse materialUsed for dull, non-reflecting materials or mesh emitters.'s Emission slot
The Black Body emission uses Temperature (in Kelvin) and Power to control the light's color and intensity.
Figure 2: The Black Body emission node parameters
Texture - Sets the light source's efficiency to either a value or texture. Keep in mind that real-world lights aren't 100% efficient at delivering power at their specified wattage - a 100-watt light bulb doesn't deliver 100 watts of light. This parameter enters the real-world values.
Power - The light source's wattage. You should set each light to their real-world wattage - for example, set a desk lamp to 25 watts, a ceiling lamp to 100 watts, and an LED light to 0.25 watts.
Surface Brightness - Causes emitters to keep a constant Surface Brightness, independent of the emitter's surface area.
Keep Instance Power - Enabling this option with Surface Brightness disabled and Uniform Scaling applied to the object causes Power to remain constant.
Double Sided - Allows emitters to emit light from the front and back sides.
Figure 3: Comparison of the Double Sided parameter when enabled and disabled
Temperature - The temperature (in Kelvin) of the Black Body emission's emitted light.
Normalize - Ensures all the normal vectors have the same length for the Black Body emission to keep the luminance of the Black Body's emitted light constant if the temperature varies.
Distribution - Controls the light pattern. This can be set to an Image (Grayscale or RGB) so you can load an Image texture 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/. file. The Image texture’s Projection map then adjusts the light's orientation or direction.
Sampling Rate - Choose what light sources receive more samples. Adjusting the light source Sampling Rates in the scene leads to a better balance between light sources. You can set the Sampling Rate to 0, which means the direct light calculation excludes the emitter.
Light Pass ID - The ID for the light pass that captures the emitter's contribution. It works with the Light Pass ID render element.
Visible On Diffuse - Makes the light source visible on diffuse surfaces. This is enabled by default. You can enable or disable the Black Body or Texture emission's light sources from casting illumination or shadows on Diffuse objects. Disabling this option disables emission - it isn't visible in diffuse reflections, but it is visible in specular reflections. It is also excluded from the direct light calculation.
Figure 4: The Visible On Diffuse option when enabled and disabled
Visible On SpecularAmount of specular reflection, or the mirror-like reflection of light photons at the same angle. Used for transparent materials such as glass and water. - Makes the light source visible on specular surfaces. This is enabled by default. You can hide emitters on specular reflections or refractions only.
Figure 5: The Visible On Specular option when enabled and disabled
Transparent Emission - Lets the light source cast illumination on Diffuse objects, even if the light source is on a Transparent material.
Cast Shadows - Enables the light source to cast light and shadows on diffuse surfaces, and it disables direct light shadows for Mesh emitters. This option has an effect if the emitter is included in the direct light calculation, or when the Sampling Rate is greater than 0. This option is enabled by default.
Note: Most of the Emission parameters are common between Texture and Black Body emissions. The main difference is if the color comes from the Black Body temperature, or from the Diffuse material's texture settings.