Houdini plugin - Lights

Emitters are part of the material system in Maxwell Render which makes possible to mix emitters with a material. For example, if a glass material is applied to a light bulb with the emitter turned on, it will shine light on the scene just like a regular emitter. But when the emitter is turned off, it will reveal the glass bulb material. Only one emitter component per layer is allowed.

Emitter materials can be defined in three different ways:

Custom: allows users to set the Color and the Intensity of your light separately. Color can be set in RBG, HSV or XYZ scales, or correlated to a Kelvin value. Intensity (or Luminance) can be set in a number of different ways described later in this section. An IES / Eulumdat file using measured lighting data can be also specified.
Temperature: in Kelvin degrees, the temperature of the light source determines both the color and its intensity. Colder temperatures (near 3000°K) emit reddish, low-intensity light, while higher temperatures (near 9000°K) emit blue, bright light.
HDR image: high dynamic range image which emits light from the emitter surface. HDR, EXR or MXI formats are accepted.

Custom properties

Custom emitters can be defined using the following parameters:

Load Preset: Maxwell Render provides some emitter presets of standard type light sources. These presets will change the color as well as the intensity of the emitter.
Color Type: specifies how the light color is set:

RGB: specifies the color of the emitted light.
Correlated (K): specifies color as a temperature value in Kelvin. Low Kelvin temperatures are reddish, 6500°K is considered white, and higher values will produce a bluish light.

Photometric Data: specifies the type of intensity of the light. There are several options to specify luminance:

Power and Efficacy: specifies the consumed electricity (Power) of the light source, and how efficiently it converts into visible light (Efficacy). The efficacy number specifies how many lumens are emitted per watt.
Lumen (Luminous Power): specifies the intensity in Lumens (lm) which is the SI (International System of Units) unit for luminous flux. With this option the same amount of lumens are emitted when the emitter surface is scaled. This gives the impression that the emitter is weaker from a larger area.
Lux (Illuminance): specifies the intensity in Lux which is defined as one Lumen per square meter (lm/m^2). With this option the amount of lumens increases / decreases with the scale of the emitting surface.
Candela (Luminous Intensity): specifies the power of the light emitted in a certain direction in Candela (Cd) which is the SI unit.
Luminance: specifies the power of the light in Nit which is defined as one Candela per square meter (Cd/m^2)

IES File: specifies an .ies or .eulumdat file which specifies the intensity and direction of emission of a certain light fixture. This is very useful if you want to use a certain light fixture from a manufacturer that also provides this information for it, but you don’t want to actually model the fixture itself.
Intensity: specifies the intensity of the emission defined by the IES file.

Temperature properties

The temperature of emission can be chosen in Kelvin degrees (°K). This mode affects not only the color but also the intensity of the emission. A higher temperature will make the emission stronger and bluer. The color will change from red (low temperature) to orange, to yellowish, to white, and finally blue (high temperature).

HDR image properties

This option allows users to texture an emitter with a MXI / HDR / EXR image. Low dynamic range image (such as jpeg) can also be used by converting it from 8 bits to 32 bits. See the HDR Image chapter in the Maxell Render manual for more information about this feature.

Houdini light node

The plug-in translates Houdini’s hlight node to Maxwell Render with creating the appropriate geometry and applying an emitter material to it. The used parameters are summarized in the following tables:

Houdini hlight node	Maxwell light geometry
Type: point	Sphere with radius of 0.05

Houdini hlight node	Maxwell light geometry
Type: line	Rectangle with width of 0.05
Area Size X	Height

Houdini hlight node	Maxwell light geometry
Type: grid	Rectangle
Area Size	Size
Single Sided	Single / double sided surface
Reverse Emission Direction	Surface normals when single sided

Houdini hlight node	Maxwell light geometry
Type: disk	Disk
Area Size	Size
Single Sided	Single / double sided surface
Reverse Emission Direction	Surface normals when single sided

Houdini hlight node	Maxwell light geometry
Type: sphere	Sphere
Area Size X	Radius X, Z
Area Size Y	Radius Y

Houdini hlight node	Maxwell light geometry
Type: geometry	Emitter is assigned to the given object, when it is translated to Maxwell.
Render Light Geometry	Hidden from Camera, Hidden from Reflections / Refractions

The emitter is generated from the following parameters:

Houdini hlight node

Maxwell emitter material

Light Color

Color

Light Intensity

Normalize Light Intensity To Area

Intensity translated linearly in the following intervals:

[0 ; 0.1] -> [0 ; 10^4]

[0.1 ; 1] -> [10^4 ; 10^5]

[1 ; 10] -> [10^5 ; 10^7]

Set as Luminous Intensity (Candela) for:

point or line type
rectangle or disk type when Normalize Light Intensity To Area is turned on

Set as Luminance for:

sphere or geometry type
rectangle or disk type when Normalize Light Intensity To Area is turned off

Spot light

If the Enable Spot Light option is checked, the plug-in generates a cone with an emitting object inside, depending on the type of the light (Point light has a little sphere, Disk light has a disk, etc.). The angle of the cone is defined by the Cone Angle parameter, the penumbra angle is translated from the Cone Delta parameter. An emitter material is generated as described above and applied only on the object inside the cone. A diffuse grey material is applied on the occluder cone.