LightTools Enewsletter

Quick Tip: NURBS Curves in LightTools

LightTools provides numerous modeling aids such as solid modeling, Boolean operations, reference geometry, etc. Included with the reference geometry tools are non-uniform rational basis spline (NURBS) curves. NURBS curves can enhance your workflow in many ways, and they can also be used for purposes such as optimization. You can access the NURBS curve tools by selecting the menu Insert > Reference Geometry or clicking 2D Objects > Draw Line on the command palette.

What is a NURBS Curve?

You can find a good description of NURBS curves here:

While the mathematical aspects of NURBS curves can be difficult to understand, LightTools presents them in a simple way for modeling needs. No extensive knowledge of NURBS curves is necessary to use them in LightTools. A NURBS curve exposes a series of control points that can be used to change the shape of the curve.

What can I do with a NURBS curve in LightTools?

There are many ways you can use NURBS curves to aid your design process. Some common use cases are described in the examples below.

  • Light Guides Using Swept Geometry
  • Convert wireframe curves to NURBS
  • Perform an Edge Extraction

With a NURBS curve, you can create a Swept primitive that will follow the curve’s path. To do this, select the curve, right-click, and choose Sweep Along Wireframe on the shortcut menu.

This creates the default Swept object profile along the NURBS curve.

The new Swept Primitive is automatically linked to the NURBS curve so that when you edit the NURBS curve, the associated Swept primitive also changes.

The cross-section of the Swept primitive can have any shape.

Convert wireframe curves to NURBS

When you export CAD models from CAD packages, you can also include reference geometry/curves as wireframe objects. These objects can be imported into LightTools as wireframe objects, but they are not editable; by converting the wireframe objects into NURBS curves, you can create an editable NURBS curve in LightTools without losing the original curve profile from the wireframe object.

Select the wireframe object and click the ToNURBS button to create an equivalent NURBS curve.

Perform an Edge Extraction

If you are working with CAD-imported geometry, and you want to know the actual surface profile, or you want to regenerate the geometry in LightTools so that you can modify it, you can use the Edge Extraction tool to create NURBS curves that represent surface profile(s).

Select the surface you want and click the Edge Extraction button.

As an example, consider the geometry of an LED collimator.

You can use edge extraction to get NURBS curves that follow surface profiles you want. The pictures above do not include edge curves for the entrance and exit ports of the collimator.

How to evaluate a NURBS curve

By default, a NURBS curve exposes all the control points. But control points do not directly represent the actual path of the curve; for this, you need to evaluate the curve.

The Curve Evaluator window provides a way to evaluate points on the curve using a parameter, T. The T parameter has a range of 0 to 1, regardless of the actual path length or the shape of the curve.

There are two ways you can use the T parameter to evaluate the curve for a series of points.

1. Use the Parameter Analyzer:

a. Add the T parameter as an Optimization Variable.

b. Add X, Y, Z points (calculated values) as merit function items. Note that if the curve is in one plane then you need only two values.

c. Run the Parameter Analyzer to evaluate the curve and collect data.

Parameter Analyzer Settings


Y and Z Data Combined (Excel Plot)

2. Use a macro to directly access the T parameter and X, Y, Z values. Code examples are shown below.

The following MATLAB function can be used to establish the link between LightTools and MATLAB. The functional form allows you to just include a single line in your code where you need to initialize the connection.

User Group Meetings

Join us for our annual LightTools User Group Meeting at one of two locations. This year's meetings will take place in Sunnyvale, CA, and Chicago, IL. Complimentary lunch as well as morning and afternoon refreshments will be provided for all attendees.

Sunnyvale, CA
Tuesday, September 10, 2019

9:00 a.m. - 4:30 p.m.
Synopsys Inc. Merlot Room

Chicago, IL
Thursday, September 12, 2019

9:00 a.m - 4:30 p.m.
Hilton Chicago O'Hare Airport

The LightTools Material Library is Now Available on Our Customer Portal

We add new materials to the library often, and now you can access those new materials between releases. The LightTools Material Library for non-CODE V glasses and plastics is available on our Customer Portal. 

Summary of Materials added or updated since LightTools 8.7:

  • Added 3 ALBIS diffuse polycarbonate plastics 
  • Added 5 Dow Chemical moldable-silicone resins 
  • Added 40 Evonik acrylic or PMMI plastics 
  • Added 3 SABIC polycarbonate or PEI plastics

LightTools Measured BSDF Library Updates on the Customer Portal

We have added and updated measured BSDF data and posted it on the Customer Portal. You can find the LightTools Measured BSDF Library on the Customer Portal.

Summary of Measured BSDF added or updated since LightTools 8.7:

  • Added 2 ALBIS ALCOM LB plastics
  • Added 9 Mold-Tech MT-1055 series, aluminized with topcoat
  • Added 8 Mold-Tech MT-11000 series, aluminized with topcoat
  • Added 12 SPI finishes, aluminized with topcoat
  • Updated 2 black anodized aluminum measurements 
  • Added 18 Tenibac 6000 series mold textures for moldable silicone, PMMA, and PC 
  • Added 3 Covestro Makrofol DE diffusers

Presentation: "Effects of individual particulates in optical systems using a spatially isolated contamination scattering method" live at SPIE Optics and Photonics

Katherine Calabro of the Synopsys LightTools team will present a talk detailing the paper “Effects of individual particulates in optical systems using a spatially isolated contamination scattering method,” co-authored with Mike Zollers.

This presentation will discuss the standard developed by the Institute of Environmental Sciences and Technology (IEST) most commonly used to define the typical sizes and density of particulates on a surface. This standard can then be used to create a BSDF profile of the contaminated surface and simulate the effects of the contaminants. This approach is limited by scattering events that occur stochastically, with no spatial consistency. In this work, a more realistic modeling approach is examined, considering particulates to be stationary, it is possible to isolate the effects of an individual particle, which can be especially useful for small scale systems. A variety of application designs are investigated through the use of computer simulation to demonstrate the advantages of the isolated contamination scattering approach.

Attend this live talk August 13, 2019 at 11:50 a.m. in the “Novel Optical Systems” conference at SPIE Optics and Photonics, located in the San Diego Convention Center.

Calendar of Events

For the latest event calendar, please go to our Events page.