RedSDK Spot Luminance

RedSDK Spot Light Luminance

About Spot Light

From the help file - "The spot light source is a centric light. It produces an isotropic lighting in all directions issued from the spot cone apex. The lighting emitted by the spot light decreases at the spot cone borders"

Basically there are two cones to be set, brighter inner cone, and a maximum cone, in this 'additional' cone area the light diminishes from the bight area to no light.




  • Intensity decay – Set the rate at which the lights power diminishes.
This can be set as No Decay, or an intensity decay using various equations.
See separate RedSDK intensity Decay page.
  • Diffuse color – Sets the diffuse color of the light.
  • Diffuse affect – Sets the relative intensity (power) of the diffused light.
Diffuse colour and affect, do a similar job in greyscale (black to white colour), the difference comes when one uses a non grey colour, the diffuse color midpoint is the selected colour, moving the slider toward the left darkens the colour, moving towards the right lightens the colour eventually reaching white.

Diffues affect is a bit like a dimmer switch moving the slider to the left lowers the intensity, towards the right increases the intensity, Note, moving either the diffuse colour or the diffuse affect towards the left (black or 0 can mean virtually eliminating the light .

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  • Specular color – Sets the specular color of the light.
  • Specular affect – Sets the relative intensity (power) of the Specular light.
Specular works with pen / brush colour objects when no material is attached, it is ignored when an object has a material, the specular (bright spot) varies with the shape of the object, moving the affect slider to the right (100) brightens the specular part, moving to the left (0) darkens / eliminates it.

The specular colour reacts with the object colour, which means the actual colour at render time may not be the same as the specular colour applied, in the same way colour varies in a paint program when using multiply, add, etc.

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  • Pos – This Sets the X,Y,Z position of the light relative to the objects being used as the luminance source, it sets the source position where 0,0,0 = the centre of extents of the object, this needs to be remembered if the source object is a box, sphere etc. it becomes important when shadows is turned on.

in the images below the sphere is 160 units radius.


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  • Dir – Sets the X,Y,Z direction of the light relative to the position.
Dir determines the direction where the light will be pointing relative to the source object extents axes, in the examples above, the source objects 'Z' axes is pointing towards the lights destination, therefore Dir is set as 0,0,1.

To force the light at an angle other that the normal x,y,z axes, one adds a figure in a second column, for example 1,0,1

Image Image

  • Top – Defines a second axis which is perpendicular to the direction used for the rotation if the lights display is not circular.
There would be few occasions when this would be needed as a spot light is a circular light irrespective of the source object shape,

  • Spot Angle
  • Additional Spot Angle
Spot angle and additional spot angle are used to set the angle at which the light exits the source objects centre of extents or position if it has been changed.

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  • Radial Intensity Decay
The Radial Intensity Decay appears to alters the spot and additional angles, it is not known at this time what equation is used to calculate the new angles.

Image Image Image

  • Shadows – Sets whether the light will generate shadows or not.
  • Shadow Color – Specifies the color of shadows created by the light.
in most circumstances the shadow colour would be left at grey scale (black to white), the shadow colour has the effect of muting the beam light after is passes through an object

Unfortunately shadows are not working correctly on my computer at present, therefore no images of its use have been included..

  • Shadow Map – Shadow maps are generated by testing whether or not each specific pixel is visible from the light source. This accomplished by comparing each pixel to a depth image (z-buffer) of the light source's view, stored in the form of a texture file. Shadow maps can accelerate the rendering of shadows, but usually as the cost of some quality.
  • Shadow Map Resolution – Sets the resolution of the shadow map. Values must be a multiples of 2.
  • Shadow Map Blur – Sets a blur factor on the shadow map, reducing jagged edges and transitions.

Because shadow map compares depth map pixels rather than computing each pixel from the light source at render time, shadow maps can be faster that other render modes, however the resolution of the depth map plays an important part in how the shadows appear, if the shadow resolution is too low the shadow can be pixelated, however increasing the resolution too high can be a little slower to render

  • Intensity Decay
The final setting for the Spot light is Intensity / intensity decay, this is accessed by clicking the '+' sign against the light within the render manager, the properties differ depending on which intensity decay is set in the main section, if No Decay is set it is used to increasing / decrease the intensity, i.e. the brightness of the light, when set to a decay equation, it adjusts the decay.
See RedSDK Intensity Decay page for options.


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Contributors to this page: AndyUK .
Page last modified on Tuesday 07 of March, 2017 05:04:34 PST by AndyUK.