Lumileds LED
  • Illumination Techniques

Modeling LEDs with Ray Files in Optical Design

In most optical designs, accurate light-source representation plays a critical role in achieving reliable simulation results. One effective and widely used method for LED source modeling is the use of ray files provided by LED manufacturers such as Lumileds.

Ray files describe the optical emission of a light source using a large collection of rays, eliminating the need to model the LED’s internal physical structure. Each ray is defined by:

(x,y,z,l,m,n,F)

where:

  • (x, y, z) are the ray starting coordinates
  • (l, m, n) are the direction cosines
  • F is the ray power (flux)

 

 

LUXEON Rebel Color Line Ray Files

The LUXEON Rebel Color Line offers high light output, excellent color stability, high flux density, and well-defined saturated colors. These LEDs are commonly used in:

  • Architectural and decorative lighting
  • Signaling and signage
  • Entertainment and stage lighting

Lumileds provides ray data files that represent the typical angular emission characteristics of these LEDs.

Ray files can be downloaded from https://www.lumileds.com/support/design-resources/optical

 

 

In this example, we use the LED model LXML-PB02.

Steps:

  1. Navigate to the Lumileds optical resources page
  2. Select LXML-PB02
  3. Choose the ray file compatible with OpticStudio
  4. Read and accept the disclaimer
  5. Save the ray file to your local system

Note: The provided ray files represent typical emission behavior only. They do not guarantee that every delivered LED will exactly match the emission characteristics described in the ray data.

 

Contents of the Ray File Package

The ray data is provided in a binary OpticStudio-specific format with the file extension .DAT.

Key characteristics:

  • Rays are randomly ordered
  • All rays originate slightly above the outer shell surface of the LED
  • Unless otherwise specified, ray starting points are defined in air

In addition to ray data, a mechanical CAD model is included in:

  • STEP
  • IGS
  • SLDPRT

The CAD model:

  • Is intended only for mechanical reference
  • Is not used for optical ray tracing
  • Shares the same coordinate system as the ray file

 

Importing a Monochromatic LED Ray File

In this example, the LXML-PB02 ray data is used. This is a monochromatic blue LED with:

  • Center wavelength ≈ 470 nm
  • Spectral bandwidth ≈ 23 nm

The provided OpticStudio sample file (*_sample_Zemax.zmx) includes:

  • The LED CAD model
  • The ray source positioned at the global origin
  • All recommended non-sequential settings

To begin simulation:

  1. Copy the ray file and CAD files into the appropriate OpticStudio data folders
  2. Open the provided sample file

This approach ensures a correct and consistent starting point for ray-tracing analysis.

 

System Units and Photometric Quantities

In the System Explorer, the simulation units are set to:

  • Length: mm
  • Flux: Lumen

Unless stated otherwise in the documentation, Lumileds ray file units are in millimeters.

Photometric quantities used in this simulation:

  • Luminous flux: Lumens (lm)
  • Illuminance: lm/m² (Lux)
  • Luminous intensity: lm/sr (Candela, Cd)
  • Luminance: lm/m²/sr (Cd/m² or Nit)

 

CAD Model Handling in Ray Tracing

Although the CAD model shares the same coordinate system as the ray source, it is not linked to the ray emission.

To ensure the CAD geometry does not block rays:

  • Set Rays Ignore Object = Always
  • Location: Object Properties → Type → Raytrace

This configuration allows the CAD model to remain visible for reference while being excluded from optical calculations.

However, since rays originate outside the CAD shell, it is also possible to:

  • Enable surface scattering on the LED geometry
  • Simulate light reflected from secondary optics back toward the LED
  • Model secondary back-scattering effects if required

 

Radiation Pattern Characteristics

The imported ray file accurately reproduces the LED’s far-field radiation pattern, making it suitable for:

  • Illumination uniformity analysis
  • Optical efficiency studies
  • Secondary optics design (lenses, reflectors, TIR optics)

Using manufacturer-provided ray files significantly improves simulation realism compared to simplified Lambertian or analytic source models.

 

Conclusion

Ray files provide a powerful and efficient way to model real LED emission behavior without detailed internal geometry. When combined with correct unit handling and non-sequential settings, they enable highly accurate illumination simulations suitable for both research and industrial optical design.