LightTools Enewsletter

August 2016

Quick Tip: Using Optical Contact/Cement for One-Sided Optical Properties, and other LightTools Tips and Tricks

LightTools assumes that every object is surrounded by the system’s ambient material, with the default ambient material being air. When there are surfaces that should be touching without an air gap between them, you should use the “Optical Contact” or “Cement” tools. For elements with overlapping volumes, you should set the intended immersion relationship using the Immersion Manager. Considering these settings is important for achieving realistic ray tracing results in systems where geometry has coincident surfaces and/or overlapping volumes.

When two coincident surfaces are in optical contact or cemented, each surface maintains its original optical property. It is possible for these contacted surfaces to have zones with different optical properties. The optical property used depends on the side of the surface from which a ray is incident. Using “Optical Contact” or “Cement,” it is possible to create interfaces where rays see different optical properties depending on ray direction, effectively creating a one-sided optical property.

Consider the two blocks made of air in the figure below. The right surface of the purple block has an optical property zone that is Smooth Optical. The left surface of the green block has a scattering optical property. When these two surfaces are declared to be in contact, any ray intersecting the surface from the purple block sees a smooth optical property at the contacted surface. Any ray intersecting the surface from the green block sees the scattering property.

Optical Contact/Cement

In most situations, the zones for the contacted surfaces should be the same optical property so the rays interact with the surface the same way in both directions. However, there are certain scenarios where it is advantageous to be able to define different optical properties depending on the ray direction.

One case is when you want to model the appearance of a poster in LightTools. In this example, you want to overlay a spatial pattern (i.e., a picture) and some other reflective scattering behavior. To do this in LightTools requires a minimum of two surfaces. One surface has a zone with a spatial apodization pattern. The second surface is a reflective scatterer. Rays will pass through the spatially filtered surface twice, which doubles the filter’s effect.

By using two objects with air as the material, you can define an optically contacted interface where incoming rays see the spatial filter, reflect off the scattering surface, and return through the filter surface a second time unaffected.

Poster Properties

The result is that you can perform LightTools simulations to observe the differences in behavior of different scattering surfaces. For example, here is a comparison of a poster with a diffuse (Lambertian) scatterer, and another with a semi-diffuse scatter. It is clear that there are differences in illuminance around the peripheral regions of the poster where the angle of incidence with the poster is higher:

Diffuse Scatterer/Semi Diffuse Scatterer

This topic was recently discussed in an “Effective Usage of LightTools” webinar. If you missed it, you can find this tip, along with tips for setting aim areas, analyzing data from multiple sources, and using the plot utility by reading this PDF file on the Customer Support Portal.

LightTools User Group Meetings 2016: September 13 & 20

LightTool Users Meeting

Current users of LightTools are invited to this one-day meeting, which will be presented in two U.S. cities. Learn about the latest developments in LightTools, listen to technical talks, and network with other LightTools users. LightTools User Group Meetings are currently planned for Sunnyvale, CA on September 13, and Marlborough, MA on September 20.

The following agenda is tentative (there may be minor changes in content).

  • LightTools 8.4 New Features and Future Plans
  • Heads-Up Display Applications Case Study
  • Effective Usage Of LightTools
  • Advanced Design Module Demonstrations
  • How to Get the Most out of Hybrid Tracing
  • …and more!

For more information, please contact email us at or call us at (626) 795-9101. We hope to see you there!

New LightTools User? Register for the New User Orientation Webinar on August 17

Wednesday, August 17, 2016
10:30 a.m. - 12:00 p.m. PDT (1:30 p.m. EDT)
 Find your local time
Duration: 1.5 hours

Learn LightTool

We invite new LightTools users to attend this orientation webinar, which will provide an overview of how to quickly get started with LightTools. We will also show you how to access resources that will help you use the software more effectively. Topics include:

  • How to obtain the latest LightTools software and license file from SolvNet
  • Basic functionality in LightTools, such as setting up analysis models, running simulations, and measuring performance
  • The resources available to you through LightTools Technical Support and the Customer Support Portal

LightTools for Automotive Interior Lighting: Speedometer Needle Case Study Webinar Recording

In case you missed it, please see our webinar recording of a "Speedometer Needle Case Study" on the Customer Portal. This can be viewed at any time.

If you have any questions about this webinar or LightTools features, please email us at