Light* Tutorial

Tony Quach

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  1. Radiosity Calculation


  • After all the surfaces are oriented in the right direction, the materials are assigned and the luminaires are defined, the scene is finally ready for radiosity calculation.
  • But don’t jump out of your seat just yet. You still have to set a few parameters before Light* can calculate the solution. Luckily, Light* comes with a Process Parameters Wizard to aid you. This is recommended for initial testing of a scene. When doing a final render, it is recommended that you manually set the various parameters to fine tune the solution.
  • When you’re ready, go to Process Parameters… , here you’ll see this dialog:

  • Click on the Wizard button to let Light* take you through a series of parameters. Just follow the on-screen instructions, it’s pretty self-explanatory.
  • After clicking Finish, go to Process Initiate or click on:

  • At this point, Light* will prompt you if you want to save the current .LP (preparation) file. Choose yes and let Light* initialize your scene. After initialization is finished, you’ll notice your most of the surfaces are now sub-divided. Go to File Save again. This time Light* will prompt you for another file name. Notice the extension at the bottom of the dialog. It is now .LS (solution file). Save it again with the same file name.
  • Click on the shaded mode button to view your model in shaded view:

  • Now go to Process Go to began calculation. Light* will start to calculate the light distribution of each luminaire and the light reflection of all the surfaces. If you’re fairly new to Light*, it is very neat to watch this process. It looks like each luminaire is being turned on, one at a time.
  • Notice the status line at the bottom of the screen. This tells you how many percent of light has been distributed. Allow Light* to continue its calculation until 85% of the lights are distributed. It is not necessary to go all the way to 100%. 85% will give you a fairly accurate representation of the final scene.
  • If at any time during the calculation you’re not happy with the lighting in the scene, go to Process Stop to interrupt the process. Next, you can double-click on whatever luminaire that needs changing and adjust its photometric setting.

  • At this time you can also change the materials of the surfaces if necessary. But it is advisable to reset & re-process (Go) the solution if you’re changing the materials because the reflected color of the new material won’t be updated at this point.

Note: When in the Solution stage, you can no longer move any objects in the scene because the meshing has already been processed. If you decide to move anything, you have to go back to the .LP file and move them there and re-initialize the solution.

  • When you’re done making the changes, click on Go button again to continue the calculation:

  • Here is an example of what my scene looks like at 54% completion:

  • At 83% completion this is how it look:

I am satisfied with the solution at this point.

  • If you like at this point, you can orbit / zoom around your model to check your model without having Light* recalculating everything. This is truly the beauty of radiosity processing. Since the light data is stored in the meshes themselves, you are free to move about the scene without having to re-render the scene.
  • You can also click on the Ambient button to turn on the rest of the ambient lighting in the scene:

  • Also, click on the Textures button to see how the textures look in your processed scene

  • When you’re satisfied, you’re are ready to raytrace the scene. Go to File Render

  • Here, you’re presented with a rendering dialog. I usually set my Antialiasing Samples to 5. Set the desired output resolution and name your image. Be sure you check the Ray Tracing option. Leave the default Ray Bounces value at 10. When you’re ready, click on Ok. Depending on what Antialiasing value you’ve set, the time it takes Light* to render each image will vary.
  • Although this is an easy way to raytrace an image, it is also very slow, because the image is being displayed on the screen as it’s being raytraced. The faster and more efficient way to do this is through the command line with LSRAY.EXE. This is the raytracing executable of Light* that comes with the program. This is only recommended for those who are familiar with command line driven operations.

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