Ray Path Analysis in LightTools

Transcription

1 Ray Path Analysis in LightTools 3280 East Foothill Boulevard Pasadena, California USA (626) Fax (626) World Wide Web: Copyright 2008 Optical Research Associates Copyright 2008 Optical Research Associates

2 Ray Path Feature The Ray Path feature in LightTools is a powerful analysis tool, especially for users analyzing stray light Records each individual path that rays take as they traverse the system LightTools 6.1 New Features, Slide 2

3 What is a Ray Path? A path is the sequence of surfaces and zones that rays intersect as they trace from the source to their termination point Data is collected for each path including: Surfaces and Zones that compose the path Number of rays that follow a given path Power in each path LightTools 6.1 New Features, Slide 3

4 Collecting Ray Path Data Controls for collecting Ray Path data are located on the Simulation Input page for forward simulation Check Collect Ray Path Data to collect the data Check Show Ray Paths to show the paths in the 3D Design View Indicate the number of rays to display per path LightTools 6.1 New Features, Slide 4

5 Backward Simulation Ray path data can also be collected for backward simulations Controls similar to the forward simulation are located on the Mesh or Points Simulation tabs LightTools 6.1 New Features, Slide 5

6 Ray Path Manager A Ray Path Manager is available to: Control the collection and display of the paths in the 3D Design View Display the data collected in the form of Catalogs The Ray Path Manager can be launched from Analysis > Ray Path LightTools 6.1 New Features, Slide 6

7 Ray Path Manager Interface The Ray Path Manager has a page for Controls Show, Collect and Display controls The Collect controls can limit data collection to specified catalogs during simulation, saving memory The Manager also has a listing for all available catalogs Controls Page Set Number of Rays per Path to Display Catalogs Show Catalog in 3D Design View Collect Data for a Catalog LightTools 6.1 New Features, Slide 7

8 Ray Path Catalogs Ray path listings are collected and displayed in a series of Ray Path Catalogs One catalog for the full Forward Simulation One catalog for each receiver in the model One catalog for each backward simulation Catalogs are not exclusive, so paths (full or partial) can appear in multiple catalogs Catalogs can be displayed independently in the 3D View using the Show setting This is separate from the View setting for individual paths LightTools 6.1 New Features, Slide 8

9 Forward Simulation Catalog Forward Simulation catalog lists paths from the sources to wherever the rays terminate All Forward Simulation rays are included in the Forward Simulation catalog Rays which split will generate two paths Path 1 Path 2 LightTools 6.1 New Features, Slide 9

10 Receiver Catalogs Each receiver has its own catalog Catalogs for both forward and backward receivers Lists ray paths only up to that receiver Surface interactions and ray splitting after the receiver are not counted Rays which do not intersect the receiver are not counted Path 1 Not Considered LightTools 6.1 New Features, Slide 10

11 Data Displayed in the Catalog Each catalog displays a listing of the ray paths in that catalog Data included in the listing are: Path visibility setting Color of the path in the 3D Design View Total power collected in that path Total number of rays recorded for that path Originating source for the path Final surface Full path listing Total number of rays and total power for all paths in the catalog with the visibility setting turned on LightTools 6.1 New Features, Slide 11

12 Ray Path Catalog Interface LightTools 6.1 New Features, Slide 12

13 Path Detail The Path Detail tab shows a tabular listing of the entire path listing for a selected path LightTools 6.1 New Features, Slide 13

14 Display A user-specified number of rays can be displayed for each path Each path displayed in a different color User can control the display of these paths LightTools 6.1 New Features, Slide 14

15 Visibility Toggle By checking and un-checking the Visibility checkbox, the user can control which ray paths are displayed LightTools 6.1 New Features, Slide 15

16 Ray Path Filter A Ray Path receiver filter is available Accepts only rays from visible ray paths in the receivers catalog All Paths Visible Three Paths Visible LightTools 6.1 New Features, Slide 16

17 Ray Path Analyzer A Ray Path Analyzer utility is available to adjust path visibility based on surface and zone intersections Logic such as and, or, & not can be applied Found under Tools>Utility Library>Receivers LightTools 6.1 New Features, Slide 17

18 Helmet Mounted Display Helmet (on a hidden layer) Eyeball Beam Splitter Combiner Lens Projection Optics Ray Path Example, Slide 18

19 Methodology The example used to demonstrate the power of the ray path feature is a Helmet Mounded Display (HMD) Specific to this example is the combiner lens and splitter What is important to understand is how much scattered sun light enters the pilots eye as compared to the light from either the display or outside world as seen through the primary viewing path. Ray Path Example, Slide 19

20 Methodology cont. Backward ray tracing will be used to improve simulation efficiency Ray path will help us understand where the light is coming from and the magnitude of the light The Ray Path Analyzer will be used to help us sort the optical paths and identify problem surfaces The optical designer can then make a decision, whether or not to change the design based on this knowledge Ray Path Example, Slide 20

21 HMD How it Works An image of the display is projected onto the beam splitter from below. A special coating on the beam splitter reflects the image onto the combiner which reflects the light back through the splitter onto the eye. The combiner also afocalizes the light Ray Path Example, Slide 21

22 HMD How it Works, cont. In addition, the eye can see through the splitter and combiner into the field of view. Thus an image of the display overlaid on the field of view. The pilot sees the display and the field of view at the same time. Ray Path Example, Slide 22

23 HMD What do we want to know? We would like to know if light from the sun can enter the optical system at oblique angles (i.e. off a mount, or the edge of a lens) and cause a distraction or even worse damage to the eye. Ray path can help Ray Path Example, Slide 23

24 Backward Ray Trace A receiver is placed on a dummy surface just at the pupil of the eye A backward intensity mesh has been added to this receiver IES Type C Angular extent from 0 to 45 degrees Aim area is set on the Beam Splitter and oversized to allow rays to be traced around the splitter A Ray Path Filter is added to the receiver to help identify contributions from various paths Ray Path Example, Slide 24

25 Source A large hollow hemisphere is set outside the system and the inner surface is set to be a Lambertian emitter Provides an even sky illumination The source is hidden to avoid visual clutter Ray Path Example, Slide 25

26 Trace Ray Paths Light from the eye receiver is traced outward to the source. Light that reaches the source would be light that could reach the eye from the sun. The mesh represents the perceived intensity of a diffuse sky as seen by the user through the display device Ray Path allows us to explore stray paths to find ones with significant intensity Ray Path Example, Slide 26

27 Backward Intensity Result The intensity result from the backward ray trace is shown here with all paths active Primary Field of View Contributions from Various Stray Light Paths Ray Path Example, Slide 27

28 Primary Viewing Path Using the Analysis> Ray Path we can quickly identify the primary viewing path and note its contribution on the Intensity Raster Ray Path Example, Slide 28

29 Stray Light Paths Turning off the visibility of the main path we can easily see the contribution from all the other paths Ray Path Example, Slide 29

30 Primary Stray Light Paths By turning on the visibility of each path in turn we can identify the primary stray light paths The top three primary paths, determined by flux, are: Direct line of sight rays, shown in purple Rays that hit the splitter but not the combiner, shown in red Rays that miss the splitter but hit the combiner, shown in dark blue Ray Path Example, Slide 30

31 Secondary Stray Light Paths We can eliminate the contributions of the main viewing path and the three primary stray light paths to see the remaining stray light contributions Areas of concern Ray Path Example, Slide 31

32 Area of Concern An examination of the remaining stray paths reveal that three of the most energetic remaining paths contribute to the two concerning areas Significantly, these three paths all TIR off of the outer edge of the combiner (sometimes twice) Ray Path Example, Slide 32

33 Ray Path Analyzer To determine all the ray paths that intersect a specific surface, or several surfaces run the Ray Path utility. In this case, all the paths that intersect the Combiner edge surface Found in the Tools>Utility Library under the Receivers category Ray Path Example, Slide 33

34 Select the Edge Surface In the Ray Path Analyzer select the Combiner> CombinerEdgeSurface> BareSurface and Add to Path Select the Receiver and select the BWD_Intensity Mesh Click Run to run the filter This sets the visibility flag to on for all paths that meet the criteria Ray Path Example, Slide 34

35 Ray Path Analyzer Results After running the Ray Path Analyzer we can see all the paths that intersect the Combiner edge surface We have identified this surface as a critical source of stray light and action could now be taken to modify the surface to reduce its effect. Ray Path Example, Slide 35

36 Conclusion The Ray Path feature in LightTools offers a means to do detailed analysis of how light passes through your system Paths are cataloged for the simulation as a whole and also for each individual receiver and backward simulation The Ray Path Analyzer provides a powerful means to quickly sort through large catalogs based on user-defined criteria The Ray Path Filter allows you to easily visualize the effects of individual paths or select groups of paths Ray Path Example, Slide 36