Category: mental ray > Light
Shader Family: Light
Output: Color
Physical Sun (mia)
This shader is intended to be used together with the mia_physicalsky shader to enable physically plausible daylight simulations and accurate renderings of daylight scenarios.
The Physical Sun shader determines the color and intensity of the sunlight, as well as emitting photons from the sun. The
shader should be applied as a light shader and photon emission shader on a directional light source (it does not work on any
other light type).
Some parameters exist in both the Physical Sun and Physical Sky shaders and all do the same thing. For physical correctness,
you need to keep these parameters in sync with each other in both shaders. For example, a sun with a different haze value
than the sky cannot be guaranteed to be physically plausible. The most important common parameters are those that drive the
entire shading and colorization models: Haze, Red-Blue Shift, and Saturation.
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The name of the shader node displayed in the render tree. Enter any name you like, or leave the default.
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Activates this shader.
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A scalar multiplier for the light output. The default value is 1. You might want to turn down the multiplier to something
like 0.01 as the default value is somewhat strong.
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Converts the output to something other than true photometric units. If this value is 1 1 1, both the values returned by the
mental ray shader API functions (for the sunlight) and (for the skylight), when sent through the function, will numerically match photometric values in lux.
Since the intensity of the sun outside the atmosphere is calibrated to 127500 lux, this is very bright when seen compared
to a more classic rendering, where light intensities generally range from 0 to 1. The RGB Unit Conversion parameter is applied
as a multiplier and should be set to a value below 1 (such as 0.001 0.001 0.001) to convert the raw lux value to something
more manageable.
For convenience, the value of 0 0 0 is internally set so that 80000 lux (approximately the amount of light on a sunny day)
equals the classic light level of 1.
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Sets the amount of haze in the air. The range is from 0 (a completely clear day) to 15 (extremely overcast or like a sand
storm). The haze influences the intensity and color of the sky and horizon, intensity and color of sunlight, softness of the
sun's shadows, softness of the glow around the sun, and the strength of the aerial perspective.
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Controls the redness of the light. The default value of 0 is the physically correct value, but you can change that with this
parameter. The range is from -1 (extremely blue) to 1 (extremely red).
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Controls the saturation, where 1 is the physically calculated saturation level. The range is from 0 (black and white) to 2
(extremely boosted saturation).
If you are using an HDR background, you can set the Saturation to zero because you probably don't need the "sun color".
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Sets the level of the horizon. The default value of 0 puts the horizon at a standard height, but you may need to change this
to accommodate different rendering locations, such as the view from the top of a mountain or skyscraper.
The horizon doesn't actually exist at any specific "height" in 3D space — it is just a shading effect for rays that go below
a certain angle, which you can change with this parameter. The total range is from -10 (the horizon is straight down) to 10
(the horizon is at the zenith), but smaller values are more useful; for example, -0.2 pushes the horizon down just below the
edge of a finite visible ground plane.
This parameter affects not only the visual representation of the horizon in the Physical Sky shader, but also the color of
the Physical Sun itself.
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The softness level for soft shadows. A value of 1 matches the softness of real solar shadows most accurately. Lower values
makes the shadows sharper, while higher values make them softer.
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The number of shadow samples for the soft shadows. If set to 0, no soft shadows are generated.
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When photon_bbox_min and photon_bbox_max are left set to 0,0,0 the photon bounding box will be calculated automatically by
the shader. If these options are set to a non-zero value, they define a bounding box in the coordinate system of the light
within which photons are aimed. This can be used to "focus" global illumination photons on a particular area-of-interest.
For example, if you have modelled a huge city as a backdrop, but you are only rendering the interior of a room, mental ray
will by default shoot photons over the entire city and maybe only a few will find their way into the room. With the photon_bbox_max
and photon_bbox_min parameters you can focus the photon emission of the mia_physicalsun to only aim at the window in question,
greatly speeding up and enhancing the quality of the interior rendering.
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Defines the bounding box minimum in the coordinate system of the light within which photons are aimed.
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Defines the bounding box maximum in the coordinate system of the light within which photons are aimed.
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Enables the automatic calculation of energy and color of the photons. When on, the light source does not need to have a valid
energy value that matches that of the sun (however, it needs a non-zero energy value or else photon emission is disabled by
mental ray). When off, the photons have an energy as defined by the light's energy value.
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Defines what constitutes "up". In Softimage, the Y axis is "up" and this parameter should be on.
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If illuminance_mode is 0 (zero), the default solar intensity is used (calculated internally based on the haze, solar angle,
optical air mass, etc.).
If illuminance_mode is 1, the sun light will have the direct normal illuminance (in lux) set by the direct_normal_illuminance
parameter. The color of the sunlight is still driven by the haze as before, only the intensity is modified.
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Specifies the direct normal illuminance (in lux) of the sunlight when the illuminance_mode is set to 1.
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Render Tree Usage
This shader is intended to be used together with the mia_physicalsky shader. You can also use it in conjunction with the shader mia_material.
This shader is applied to a directional light that represents the sun, and the mia_physicalsky shader is used as the scene's
camera environment shader. The environment shader should be used to illuminate the scene with the help of final gathering,
and bounced light from the sun can be handled either by final gathering diffuse light that is bounced or via global illumination
(photons).
Connect this shader to the Light node's Light Shader input.