LED manufacturer OSRAM Opto Semiconductors provides comprehensive ray-tracing data for its range of products available in OpticStudio format. This article explains how to access and use that data.
Authored By Mark Nicholson, Regina Dürr
Updated Feb 2024 By Alexander Guenther
In most optical designs, the exact representation of light sources plays an important role. One possibility for light source modelling . represent the emission of the light source by a large number of rays without needing to model internal components. Each ray is described by three starting and three propagation coordinates, as well as power: (x, y, z, l, m, n, F).
Ray files can be found on the homepage (https://ams-osram.com/) of -OSRAM AG under “Support / Tools”. Selecting the link “Optical Simulation / Ray Files / Package CAD Data” forwards a page with several subfolders. Direct access to this page is by using the link www.osram-os.com/ray-files. The subfolders within list the different product types of the respective application area. After selecting the group of interest, discrete LED names are shown which, in turn, are the links to the individual ray files.
Fig. 1: website with subfolder SYNIOS®.
In this example, we will download the data for the "SYNIOS® P2720” KY DMLQ32.23. The ray file is available in several data formats. Click on the link to the ray file in compatible OpticStudio format, named *_Zemax.zip. Next, read and agree to the disclaimer, then “Save” the file to your computer.
Fig. 2: Download ray file for desired product in OpticStudio format.
The ray files provided are only exemplary and imply the typical emission characteristic of this LED type. For this reason, the files provided do not guarantee that a LED which has been delivered shows exactly the same emission characteristic indicated in the ray file package.
The data comes as a zip-file. It contains ray files with a different number of rays, a CAD model, LED spectra, an OpticStudio (file extension.zmx) sample file and a documentation file.
The ray files are available in three different sizes: 100000, 500000 and 5000000 rays. They are provided in a binary data format specific to OpticStudio with file extension .DAT. The rays in the ray file are randomly ordered. The starting points for all rays are slightly above the outer shell surface of the LED. If not intended otherwise, the starting points of the rays need to be specified in air.
The CAD model is provided in three different formats: STEP, IGS and SLDPRT. It is a placeholder for mechanical design only and not intended for optical raytracing calculations. CAD models and ray files always share the same coordinate system.
At least one radiometric color spectrum is included as the SPCD-file. The SPCD format is an OpticStudio specific data format for spectrum data; it is a text format which can be viewed and edited in any text editor.
The information file in PDF format depicts the orientation of the ray file. This file contains a mechanical drawing of the LED, with an (x,y,z) axis system superimposed. It shows the orientation and location of the LED with respect to the original coordinate system. The documentation file also contains information about the “virtual focus” of the specific ray file, which is defined as the point, having the smallest accumulated distance in 3D space to all the rays of the rayset weighted with the ray intensity. The coordinates are provided with respect to the previously mentioned coordinate system.
In addition, an OpticStudio sample file is included in the data package showing the recommended settings and alignment of ray files and CAD model. A guidance on how to use the sample OpticStudio Lens File is given in the following section.
Fig. 3: Content of the OpticStudio (Zemax) ray file package.
In this example, we use ray data of the “SYNIOS® P2720” KY DMLQ32.23. It is a monochromatic LED with its spectrum centered at approximately 590 nm and a spectral width of ~ 20 nm.
The OpticStudio sample file (named *_sample_Zemax.zmx) includes the CAD model and the ray file positioned at the global origin. It comprises all recommended settings and provides an easy to use starting point for an optical raytracing calculation. Therefore, it is only required to copy the necessary files in the certain data folders of OpticStudio and to open the sample file. We will do this in the following and review the settings made in the file.
Start OpticStudio, select Setup...Project Preferences and check the location of the OpticStudio objects directory.
Fig. 4: OpticStudio data folders.
Copy the ray files (named rayfile_*_Zemax.DAT) from the ray data package to the subdirectory “Sources\Source Files” within the OpticStudio Objects directory and the spectrum file (named *_spectrum.spcd) to the subdirectory “Sources\Spectrum Files”. The sample file makes use of the CAD model in STEP format, hence the STEP file from the ray file package must be copied to the “CAD Files” subdirectory in the OpticStudio Objects directory.
Now open the OpticStudio sample Lens file. If all files have been copied in the correct subfolders the sample file will open without any error message.
The non-sequential component editor (NSCE) shows two components – the Source File and the CAD model. Both are at the same position, which ensures that the alignment of both components relative to each other is correct.
Fig. 5: Non-Sequential component editor for OpticStudio sample file. (Right-click the image and open in a new tab for higher resolution).
Here is the 3D geometry of the two objects displayed in the NSC Shaded Model viewer. The rays are starting close to the outer shell of the CAD model.
Fig. 6: NSC Shaded Model view of ray file and CAD model.
In the System Explorer, the units are set to “Lumen” and “mm.” If not intended otherwise in the pdf documentation, units in the ray files are mm. The luminous flux of the KY DMLQ32.23 is measured in units of Lumens so we choose that unit for this simulation. Illuminance is therefore measured in terms of lm/m2, or Lux. Luminous intensity is measured in Lumens/Steradian or Candela (Cd). Luminance is measured in lm/m2/sr, or Cd/m2, which is sometimes referred to as a Nit.
Fig. 7: Review of system units in the System Explorer.
The Source File Object is located at the center of the global coordinate system, the ray file with 5000000 rays is linked and the power is set to the typical luminous flux of the LED. Check the object properties of the source file and you will find the linked ray file and spectrum.
Fig. 8: Ray file and spectrum file specified in the object properties of the source.
The typical Luminous flux of the LED (65 lm) is given in the Power column of the NSC Editor.
Fig. 9: Typical luminous flux of the LED is set in the power column of the NSC editor. (Right-click the image and open in a new tab for higher resolution).
The CAD model shares the same coordinates with the ray source but the coordinates are not linked. As the CAD model is for reference only, it will be ignored in the raytrace. This option for the CAD model is set in the object properties under Type...Raytrace by selecting “Rays Ignore Object = Always.” of the CAD model. However, the rays in the ray file start outside the CAD model, such that it is possible to, for example, allow the LED surface scattering properties in order to consider light back-reflected from secondary optics to the LED and again backscattered from the LED towards the optics.
Fig. 10: Object Properties of the CAD model.
You can now add a detector or any other object to the sample file and begin your raytrace analysis.
The spectra of white LEDs have at least two local maxima due to the specific generation principle of white light. The peak in the blue wavelength range has a narrow width and a peak wavelength around 450 nm. The peak in the yellow wavelength range has a wider distribution with a peak wavelength around 540-600 nm, depending on the LED type.
Fig. 11: Typical spectrum for a white OSRAM LED.
Due to the different angular characteristics of rays in the “blue” and “yellow” parts of the spectrum, a separation of the ray model into two parts is necessary. Therefore, two ray files are delivered with each white LED – one ray file for the blue and one ray file for the yellow part of the spectrum. Both ray files have the same global coordinate origin. This concept requires two Source File Objects in OpticStudio which must be placed at exactly the same (x,y,z) coordinates. The optical simulation should run simultaneously for the two ray files as for two overlapping sources.
In this example, we will use ray data of the “OSLON® Compact PL” KW CELNM3.TK. It is a white LED with typical color coordinates
Cx = 0.32 Cy = 0.33 according to CIE 1931.
As in the example given above, ray files, spectra and CAD model must be copied to the proper subfolders within the OpticStudio Objects folder.
Opening the provided sample file gives us three components in the NSC editor: the “blue” and “yellow” ray files and the CAD model. All three components are placed at the same coordinate point.
Fig. 12: Non-Sequential Component Editor for a white LED. (Right-click the image and open in a new tab for higher resolution).
The settings for system units and the CAD model are the same as in the previous example for the monochromatic LED. The settings for the two Source File Objects will be discussed below. For the first source file object, the blue ray file with 5000000 rays and the blue spectrum for the color bin “5M0” are linked as can be seen in the object properties. For the second source file object, the yellow ray file and spectrum for color bin “5M0” are also linked. The simulation is done with the two sources emitting simultaneously.
The typical luminous flux of KW CELNM3.TK is 460 lm. This luminous flux must be split into a blue and a yellow contribution. The flux ratio between blue and yellow depends on the spectrum and hence is slightly different for different chromaticity coordinate groups. There are typical spectra for different chromaticity coordinate groups included in the ray file package. Every spectrum is split into a blue and yellow part. The luminous flux ratio is determined by integration of the blue and yellow part of the spectrum. The typical ratio for three chromaticity coordinate groups are shown in the rayfile information file.
Fig. 13: Flux ratios for different chromaticity coordinate groups as given in the ray file information document.
In this example, 7.82 lm is used for the blue and 452.18 lm is used for the yellow part, corresponding to the relative photometric flux 0.017 and 0.983, given in the pdf, and a typical total flux of 460 lm.
This procedure also enables simulating the potential impact of other color bins on the optical performance, for example, of a secondary lens system. For that, the flux has to be changed following the values given in the pdf and the corresponding spectra must be linked.
Ray measurement files
Ray measurement files can be used to create ray files with different ray count. These files are created by the measurement system itself. The measurement files are contained in the file named *.TTR.zip which is available for download in same folder as the OpticStudio ray files.
When opening the *TTR.zip package, the measurement file(s) (named *_TTR.ttr) will be found. To access data from the file, a special software called Converter801 is required. This software can be downloaded from the homepage of TechnoTeam Bildverarbeitung GmbH (www.technoteam.de). To process measurement files correctly, Converter801 Version 1.8.0 or higher is required.
After opening the measurement file with Converter801, different data sections can be accessed. The file provides common information about the LED and the measurement itself. The luminous intensity distribution for every polar scan can be displayed. Another section shows the rays of the camera images. In this section a visualization of the measured rays for every camera image is shown. A section for additional data contains on the one hand the data which can be found in the *.zip package too, on the other hand some luminance images. These luminance images are measured additionally to create an impression of the light source.
Before the data of a measurement file (*.ttr) can be used in simulation software, it needs to be converted into a rayfile. A geometry that defines the starting points of the rays is therefore required. A specific default geometry setting is included with in the measurement file. Further there are coordinate transformation values included. By using these coordinate transformation values, rayfiles are created with an orientation as shown in the information file, matching the other rayfiles in the *.zip packages. Therefore, it is recommended to use the default values for geometry and coordinate transformation during the creation of a rayfile.
Rayfiles can be created by direct conversion or by batch processing. The number of rays and the flux can be adjusted. A spectral signature can be added by using an external spectrum file or the spectrum which is included within the measurement file.