RedSDK Rect Physical Luminance

RedSDK Rectangular Physical Light Luminance

Work In Progress - Editing and pictures to be completed shortly as of 01_Feb_2016.
About Rectangular Physical Light

From the help files - A Physical Rectangle light uses the definition of light sources from physical parameters issued from lamp manufacturers. A Physical Rectangle light uses a rectangle that defines the light surface that will emit light in the scene. Physical lights are rendered on the CPU using sampling and are approximated on the GPU. There are two possible approximations for a physical light on the GPU:
  • If the physical light is linked to a rectangular mesh, then the physical light is automatically turned into an Area light.
  • If the physical light is linked to a mesh with any other geometric shape, then the physical light is automatically turned into a Point light.


The rectangular Physical light has more parameters than the standard physical light, it has position and direction which can be set.


  • Power – Sets the power of the light in Watts.
  • Luminous Efficiency – Sets the luminous efficiency of the light in percentage (%).
Power is simply like changing a lightbulb for higher or lower wattage, for Luminance efficiency See internet search for full description, in TC it appears like a diffuse value, lowering the efficiency of the light produces a reduction in brightness.

Image Image

  • Intensity decay – Set the rate at which the lights power diminishes.
Not much choice here s its fixed at Natural Quadratic.

  • Color – Sets the color of the light.
Changes the light colour for specific affect, normally one would leave at a greyscale (black to white) colour, ts is possible to change it to produce other effects like serpia, below its changed to red to show the dramatic change.


  • Color Temperature – Alternate color value which supports definition of the color by temperature in Kelvin.
Instead of changing the colour , one can set the temperature of the light, however different websites use various ideas of what the temperature represents, so the image below was produced as an approximation with TC, obviously this will vary on different computer monitors. Using luminance color values - unlike using 'color', can produce a variable of colour rather than a single colour.

Image Image

  • Color Affect – Sets the relative intensity (power) of the color light.
Lowering the colour affect diffuses the colour, increasing the colur affect increases the brightness of the colour.


  • Samples Count – Sets the maximum number of light samples.
Increasing the sample may (or may not) produce a more accurate render but can increase rendering time.

  • Pos – Sets the X,Y,Z position of the light relative to the object to which it is attached.
  • Dir – Sets the X,Y,Z direction of the light relative to the position.
  • Top – Defines a second axis which is perpendicular to the direction, used for the rotation, if the lights display is not circular.
  • Samples Count – Sets the number of samples used to populate the light surface. Must be greater than 0
  • Width – Sets the width of the defining rectangle.
  • Height – Sets the height of the defining rectangle.
  • Shadows – Sets whether the light will generate shadows, or not.
  • Shadow Color – Specifies the color of shadows created by the light.
  • Texture File Name – Rather than using a single constant color for the whole light, you can setup a texture from which light color will be read. Using a texture, you can simulate projectors or complex light filters.
  • IES File Name – Manufacturers measure the behavior of their bulbs and store their directional contribution into IES files. Those files are available for most of the bulb models directly from the manufacturers' web sites. Even if IES files store information about the shape of the emitter, they are not used here.
  • Caustics – Specifies whether the light will generate caustic effects.
  • Visible Geometry - Specifies whether the physical geometry of the associate 3D objects will be seen.

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Contributors to this page: AndyUK .
Page last modified on Wednesday 08 of February, 2017 04:25:38 PST by AndyUK.