RedSDK Physical Luminance

RedSDK Physical Light Luminance

About Physical Light

From help files - A physical light uses the definition of light sources from physical parameters issued from lamp manufacturers. A physical light is associated to a mesh ( The 3D Object associated with the Luminance) that defines the light surface that will emit light in the scene. Therefore a physical light can be of any shape.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.
Different object shapes can produce different lighting, the three images below all have the same parameters and are in the same position, left = Sphere, right = Box, bottom = rectangular sheet.

Image Image Image


  • Power – Sets the power of the light in Watts.
Works the same as adding a higher wattage bulb in ones house.
  • Luminous Efficiency – luminous efficiency of the light in percentage (%).
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 because 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 variation of colour depending on the object the light hits 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.
  • Double Sided -
  • Shadows – Sets whether the light will generate shadows, or not.
  • Shadow Color – Specifies the color of shadows created by the light.
Normally left at greyscale (black to white), moving the slider to the left darkens the shadow, moving to the right (towards white) lightens the shadows, changing to another colour can look odd if not done carefully as shown below.

  • Shadow Map - turns on automatic shadow map generation, shadow maps take a snapshot from the light source and compares this to the render from the camera perspective, this can may rendering quicker, but can also reduce the quality, also shadow maps may not produce accurate renders of transparent objects,
In the image below with shadow map turned on, the shadows produced from the glass on the sink is too strong


  • 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.
Requires experimentation, texture file can be used to change / set the colour to give different effects, actual usage may be more trouble than its worth, due to the experimentation required to get the correct results.

Images used as the texture can be simple or complex, below shows two images and their outcome when used as a texture file.

Image Image Image Image
  • 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.
Caustics require a bit more thought, in that they only work if there is a material applied to an object which has its own caustics checkboxes selected, it also requireds a object to catch the caustic effect though this does not require its caustics to be ticked, (in deed it may be better not ticked), caustics works well with GI rendering but will also work with quality raytrace.

The difficulty with this 'standard' physical light is that the light direction is difficult to control.

Image Image

  • Visible Geometry - Specifies whether the physical geometry of the associate 3D objects will be seen.
Selects whether the source object is illuminated in the render, it doesn't remove the object just allows it not to show up as a bright object.

Image Image
  • Covert emitter units to metric
No idea, assume its to convert imperial fractional units to standard metric for ease of calculation.
  • Extra Scale
Accessible by clicking the '+' sign against the 'Physical' name in Render Manager, it appears to multiply the amount of light fall off, producing a darker render than standard 'Natural quadratic'.

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Contributors to this page: AndyUK .
Page last modified on Tuesday 07 of March, 2017 05:05:09 PST by AndyUK.