This Technical Description provides a detailed overview of the LightTools illumination design software available from Optical Research Associates (ORA®) for optical system modeling, illumination analysis and engineering. It is intended as a supplement to the four-color LightTools brochure.

LightTools is a state-of-the-art illumination design software program that directly represents optical entities such as sources, receivers, lenses, lightpipes, reflectors, prisms, diffractive elements, beam splitters, and diffusers in the same model and environment as mechanical components and structures. Multiple polychromatic ray traces, including ray branching at optical surfaces, simulate the real-life effect of the optical and mechanical elements on the geometric propagation of light through an optical system. The model becomes a virtual prototype allowing the user to analyze the system, perform tradeoff studies, and optimize system performance.

LightTools is available on Intel-based personal computers running Windows 2000 or XP. LightTools is licensed on a monthly or annual lease basis. Included with LightTools licenses are all updates, improvements, and documentation as they are released, as well as unlimited telephone, fax, and e-mail technical support. The customer service staff is composed of full-time technical support personnel with optical engineering backgrounds and work experience.

LightTools is modular, with one required module and several separately licensed optional modules that support specialized applications:

• Core Module (required) - Essential optical and mechanical modeling, visualization, and ray tracing capabilities
• Illumination Module (optional) - Adds sources, receivers, and analysis features for illumination design
• Imaging Path Module (optional) - Adds sequential ray tracing and special optical analysis features
• Data Exchange Modules (optional) - Add import/export capability for several industry- standard CAD file formats (IGES, STEP, SAT, CATIA V4 and V5)
• Optimization Module (optional) - Adds the ability to automatically improve the performance of an illumination system based on the criteria that you specify.
• Advanced Physics Module (optional) - Adds advanced optical modeling capabilities for cutting-edge applications.

Although the optional modules are separately licensed, when they are installed their features are fully integrated with the Core Module features and user interface. Except for a brief summary of each non-Core module, this Technical Description will therefore describe the Core Module and the optional modules in an integrated fashion. Features that are specific to a module other than the Core Module will be noted in the appropriate sections.

For additional information on specific platforms and hardware requirements, or for lease prices, call ORA or send mail to service@opticalres.com.

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LightTools enables the user to observe and analyze the propagation of light through systems containing sources, optics, and mechanical components. The Illumination Module utilizes Monte Carlo ray tracing to perform accurate modeling of the illuminance or intensity distribution anywhere in the system. Polarization, scattering, and surface reflection effects, as well as the performance of thin film coatings, can be included in the analysis. LightTools is designed to make the cycle of analyzing, altering, and retesting a system quick, simple, and intuitive so that numerous design iterations are possible, thereby reducing the need to create multiple physical prototypes.

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Combining basic solid geometric shapes (spheres, cylinders, cones, rectilinear boxes, extrusions, tapered extrusions, surfaces of revolution) with each other or with optical elements via Boolean operations (union, intersection, subtraction, trimming) permits the creation of an unlimited range of shapes for use in the system model. Users can create complex light guides, mechanical structures, trimmed lenses, segmented reflectors, and extremely irregular optical elements. No matter how complex the elements or convoluted the optical paths, ray tracing of the model in any direction, (by individual rays, ray fans, or ray grids) is possible - starting from any 3D location.

LightTools' element-based approach is a direct description of the physical form of the complete opto-mechanical system and can be used to represent both optical components and mechanical structures. The element-based approach used in LightTools is similar to that used by mechanical design and analysis engineers and by optical manufacturers with whom the optical engineer must interface. The element-based approach also permits high fidelity graphical rendering, including VRML export of the optical system, which is useful for design verification, visualization, and communication.

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LightTools uses a modern graphical interface. Model creation is done using the mouse or keyboard in combination with a hierarchical icon palette and pull-down text menus. Each icon contains a graphic on its face that describes not only the function to be performed, but the type and order of input. A toolbar of commonly used icons is continuously available.

Data can be displayed and modified using spreadsheet-like tables and component-specific dialog boxes in addition to direct manipulation of geometry.

Dynamic feedback occurs during the process of creating and modifying the model geometry through continual x, y, z coordinate updating, silhouetting and attaching of the geometry to the cursor, and "rubberbanding" of elements during the definition process.

As inputs are made by the user, the program builds an equivalent text-mode command in a field at the bottom of the active window. These commands can be viewed and even modified by the user as the model is created. Using the LightTools macro language (based on the Basic programming language) the user can automate the creation, modification, and analysis of the model.

In addition to the LightTools User Guides electronically available via Acrobat PDF format, on-line help, assistance, coaching, and messages are available via context sensitive help, context sensitive command-line messages, and continuous session monitoring in a console window.

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LightTools’ fundamental construction techniques are very similar to those in advanced mechanical CAD software programs. However, LightTools also has many features to facilitate the creation and modification of optical elements.

Basic geometric creation and editing techniques include place, move, rotate, copy, and scale of system components. Elements can be combined into logical grouping in a variety of ways. This is very useful in managing complex systems. The grouping techniques include a temporary selection group and a permanent grouping option. Once grouped, element parameters (position, color, visibility) can be modified en masse. Layers provide an additional way for the user to segregate data, usually by element type or logical sub-system.

Positioning tools include grid and "snap to" features. The grid may be visible or not, or a visible grid can be at a different resolution than the active grid. The snap feature is useful in aligning a part in relation to other geometry, including rays, or to one of the global or local axes. A depth feature allows users to work in a given plane and modify the position along the third axis. In addition to the global system coordinates, a user-defined local coordinate system can be established. This is useful in working with irregularly folded systems.

LightTools basic 3D solid primitives, sphere, ellipse, toroid, block, cylinder (including cone), extrusion and rotationally swept polyline, can be parametrically edited and inserted with any size, in any location, and at any angle. Complex objects previously defined using Boolean operations can be edited at any time (even after the object is complete); the object does not need to be deleted and recreated. Each solid can be combined with any other solid using the Boolean operations, union, intersection, and subtraction. This allows the creation of complex, as-fabricated, models, such as segmented reflectors and multifaceted lightpipes. Note that the complex elements can be either optical, mechanical, or structural components. The 3D solid modeling capabilities of LightTools with Boolean operations permit the creation of complex systems where baffle design and stray light effects can be modeled. As-built models can locate potential problem areas before expensive downstream design or manufacturing problems arise.

With the Illumination Module, volume-emitting or surface-emitting light sources of various predefined shapes can be similarly entered and even combined with mechanical and optical parts to form models of lamps, light bulbs, LEDs, and other illumination devices. These devices can also be stored as Library parts for later use. The Illumination Module is also compatible with Radiant Imaging's Radiant Sources™  source files allowing the user to spend time designing the illumination system and not worrying about lamp or source creation.

Likewise, the LightTools Core Module has standard pre-defined fold mirror and beamsplitter orientations and surface treatments so that many mirrors can be added from the icon button palette with no user refinements required. Several prism forms (Right angle, Porro, Penta, and Dove prisms), and several forms of reflective polygon spinners, are provided as basic entities in LightTools. Other complex prisms (corner cubes, Wollaston prism) are provided as library parts or can be built by the user and stored as library parts. Any shape prism is possible using the prism extrusion primitive, in combination with Boolean operations and other primitives for the purposes of beveling, truncating, or creating holes in the prism element. 

When modeling devices with repetitive or periodic structures, the array features of LightTools are very convenient. They allow a single object to be created and then duplicated in a rectangular or circular pattern with just a few data entries and mouse clicks. Luminaires and segmented reflectors are among the devices that can be easily modeled with array methods.

Another uniquely powerful feature of LightTools is the ability to "sketch in" optical elements in a 3D solid form. Rotationally symmetrical lenses can be sketched with between three and six mouse clicks, depending on lens shape. Duplicating this simple input method with traditional mechanical CAD packages is complex, time consuming, and requires Boolean operations on several spheres and a cylinder to accomplish.

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The LightTools illumination design software is a 3D solid modeler with specialized optical features and "optical accuracy." When designing or machining a mechanical part, accuracy within 20 microns may be sufficient. However, when tracing the path of light rays through an optical system, specification of the surface shapes and intersections to optical accuracy (a fraction of the wavelength of light) is necessary. Unlike some CAD programs, surface shapes in LightTools are defined with parametric formula, which facilitate the maintaining of surface shape, position, and intersection to optical accuracy for all calculations. This optical accuracy ensures that the LightTools model performs as the real system will. Illumination analysis is performed using state-of-the-art Monte Carlo techniques to help insure accurate simulation of light effects. The user has control over the simulation to  modify the receiver properties such as the number of bins and symmetry calculations to affect the simulation error estimate. Millions of rays can be traced for the Monte Carlo simulation for high precision applications such as microlithography systems.

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Non-sequential ray tracing is an inherent capability in LightTools. Traditional optical programs demand that the user specify which optical surfaces the light will hit, and in which order. This is called sequential ray tracing. LightTools supports sequential surface definitions and sequential ray tracing in imaging paths (see below). However, the LightTools default mode supports non-sequential ray tracing, where light rays are "pointed" in one direction and then propagate according to the laws of geometrical optics as they reflect, refract, diffract, or scatter off and through optical and non-optical entities. Full polarization ray trace control can be used in conjunction with user defined thin film coatings to completely model light interactions through the system.

Since optical and mechanical components are represented as solid objects in 3D space rather than as lists of surfaces, non-sequential ray tracing can be done with no additional specification by the designer (other than the need to define any special optical properties of individual surfaces, such as gratings or Lambertian scattering surfaces). Single rays, fans, and grids can be traced using a simple "point and shoot" technique. This capability is also used for defining sequential ray paths through the system model, for investigating stray light behavior, and for modeling the true effects of optical components. Polarization ray tracing can be utilized by creating polarizing elements (ideal linear polarizers and retarders or specifying the Jones or Mueller matrices for a surface) or modifying the polarization states of the ray trace. Interesting TIR or ray-splitting conditions can be quickly and easily identified and evaluated.

Non-sequential rays are also used by the Illumination Module, allowing illumination analysis on even the most complex opto-mechanical systems. The Illumination Module uses a Monte Carlo simulation to propagate non-sequential rays from random positions and directions from an unlimited number of sources. The ray data is collected on any number of receivers to allow the user to analyze the irradinance and intensity distributions of the receivers.

Optical and polarization properties can be defined for every surface of every object, and these can be modified using an information dialog box. These properties allow users to define ray direction (specular, Fresnel surface, grating, or scattering surface models), and ray amplitude (reflect/transmit, Fresnel loss, scattering, polarization states, or user defined thin film coatings). Ray direction will depend on the type of surface. Most surface types support TIR, split, reflect, absorb, etc., while others (scattering and grating surfaces) will support transmitted, reflected, or both.   

User-specified wavelengths are associated with each ray fan or grid. Multiple ray fans or grids may exist in a single model, each traced in different wavelengths. Each ray can split and branch as it encounters split surfaces (or branch multiple times when encountering a multiple-order diffractive surface). The ray trace tracks the energy percentage at each surface intersection. Energy tracking is affected by bulk absorption, polarization, and coating characteristics as well as the user-specified percentage of energy following each path at a split or branch (DRAT model, for diffract, reflect, absorb, transmit). Fresnel surface losses and scattering losses are also included when defined by the user. In the Illumination Module, each source can have its own set of wavelengths and spectral weights to define its polychromatic properties.

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LightTools has many features to assist users in visualizing the opto-mechanical model, replicating 3D phenomena via a two-dimensional computer screen.

One pane, two pane, and four pane configurations are possible. Users can quickly and easily change between these configurations at any time during a LightTools session. Multiple panes allow the user to simultaneously view the model from different viewing angles and magnifications. All panes update simultaneously. When defining, positioning, or modifying elements, users can select in any of the panes as is most appropriate or convenient.

Additional windowing capabilities include pan, zoom (magnification), and rotation of the viewing angle and position. Standard viewing angles have their own icon buttons for quick positioning. They include front, side, top, and isometric views, automatic centering and sizing of the geometry within a chosen pane or panes, and system-defined icon buttons for standard rotations around each of the x, y, and z axes. Using VRML export the user can manipulate the model in real-time with high fidelity graphics rendering.

Numerous representations of the 3D model can be viewed. Each representation is designated as a LightTools View. Views include the 2D and 3D design views, the Field Specification and Glass Map views, and tabular/spreadsheet Table views. The Imaging Path View (Image Path Module only) combines aspects of a geometric view with those of a tabular view. As many views can be open simultaneously as desired. All views update simultaneously, since they are simply reflecting changes to the single database that commonly defines them all. This is extremely important in terms of quality of the software (redundant databases and pointers between multiple databases are not required) and in terms of efficiency of computer resources.

Elements in LightTools can be displayed in wire frame, profile, hidden line, solid, and translucent renderings. Users can easily change the rendering mode any time. Solid and translucent renderings can be used simultaneously with the choice determined by surface attribute. Rays are normally displayed on all relevant 2D and 3D views, though in the case of Monte Carlo rays traced for the Illumination Module, the display of rays is by request only, since displaying rays slows performance when large numbers of rays are traced.

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Many features in LightTools differentiate the software from traditional CAD programs because they are uniquely useful to the optical and illumination engineer. Listed below are some of these features not discussed elsewhere in this Technical Description.

Lens elements can be bent so that the shapes of the surfaces change while maintaining the focal length. This can be used to investigate the relative effect of differing lens shapes on aberrations while maintaining a constant focus position. Attaching two optical surfaces is also easy. The cement tool attaches two optical surfaces on different elements while maintaining their distinct and respective optical properties. This is useful, for example, for creating cemented doublets or cube beamsplitters. The immersion feature can be used to allow objects to be immersed, or partially immersed, in optical materials other than air. This allows accurate modeling of components such as cladded fibers, flow sensors, and LEDs.

There is an extensive materials catalog for optical and mechanical materials, including ten manufacturers' glass catalogs. Three of the glass catalogs (Schott, Hoya, and Ohara) can be accessed via an interactive graphical glass map represented in the traditional Nd vs. Vd format. The glass materials fully support multiple simultaneous wavelengths. User defined materials are also supported including common optical plastic materials such as acrylic, polycarbonate, and polystyrene..

Each surface on an element can be specified as reflect, refract, TIR (total internal reflection), absorb, split, diffract, or scatter. User defined coatings (based on performance specifications) can be applied to any surface. Polarization characteristics can also be specified in terms of the Jones or Mueller matrices or by setting the surface to be an ideal linear polarizer or retarder. Clear aperture zones can be used to define the portion of the lens that is optically relevant. Reflectance, transmittance, and absorption characteristics can be defined in terms of the percent of energy in each path, allowing the tracking of energy along each path. Tabular and grid footprint displays allow for further understanding of this data. A user-definable "maximum hits per surface" feature prevents a ray from encountering any surface an unlimited number of times (as might occur in a laser cavity).

Diffractive optics support includes linear gratings, binary optics, and general radial and x,y phase polynomials. The number of multiple diffractive orders (reflective or transmissive) supported on a given diffractive surface is as great as the number that can physically propagate. Scattering surfaces may be used in any model, but are most common in illumination systems. Lambertian, Gaussian, and cosine-to-the-N-power, a mixed diffuse/specular model, and user defined scattering models are supported.

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LightTools provides graphical output in PostScript format. Tabular data can be exported in tab-delimited text format (standard spreadsheet import format). LightTools also supports its own script file definition for electronic transfer of LightTools models. DXF format and IGES wireframe export is available. Full import/export between LightTools and other CAD/CAM programs is handled through optional Data Exchange Modules via STEP, SAT, and IGES (see below).

LightTools is import/export compatible with CODE V, ORA’s industry-leading optical design software. This allows you to combine the advantages of CODE V’s extensive capabilities for diffraction analysis, optimization, and tolerancing of optical systems with LightTools’ unique ray tracing and visualization capabilities. Systems can be sketched in using LightTools, then moved into CODE V for advanced analysis, optimization, or tolerancing. Similarly, existing CODE V models can be imported into LightTools for visualization or modification. Note that because the methods of modeling optical systems are very different between LightTools and CODE V, some modeling features cannot be transferred, or will require user modifications after import.

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ORA provides comprehensive user's guides, reference guides, tutorials, and application notes with each copy of LightTools licensed. The documentation is updated regularly along with the software.

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OVERVIEW OF OPTIONAL MODULES

Illumination Module

The Illumination Module, which may optionally be licensed for use withLightTools, offers special features for the modeling and analysis of illumination systems. All of the Core Module capabilities can be used to create systems with reflectors, lenses, light pipes, integrating rods, diffusers (transmitting and/or reflecting scattering surfaces), baffles, shades, and other optical or mechanical parts. 

Multiple sources can be added to the model. Sources can be created using actual measured 3D data from Radiant Imaging to simulate the complete lamp model such as high intensity sources, luminaires, and LEDs. Point sources, surface emitters, and volume sources are also supported. Source shapes are point, cylinder, sphere, block, or toroid. Source properties include wavelengths and spectral weights, total power (radiometric or photometric), emittance direction (per surface), aim sphere (angular emittance region), spatial apodization (uniform, user defined), angular apodization (Lambertian, uniform, or user defined). Sources can be saved as library elements (either alone, or combined with optomechanical parts as in a lamp model).

Receivers are used to collect ray trace energy data for calculations. Receivers are either attached to surfaces or defined as far-field collectors for intensity (angular) calculations. Any number of receivers may be defined. Illumination simulation is based on Monte Carlo ray tracing of a user-defined number of rays from all defined sources. The ray trace tracks the energy associated with each ray, accounting for Fresnel surface losses, user-defined reflectance and transmittance, scattering losses, polarization and coating effects, and absorption. Monte Carlo ray trace data is retained in memory, allowing receiver properties to be re-defined without re-tracing the rays. 

Analysis options include irradiance on a receiver surface and intensity at a near-field or far-field receiver. The LightTools illumination analysis capability can be enhanced and expanded using the macro language feature. Macros can be created to vary any number of parameters of the model and determine the effect on the system's performance. For example a macro can be written to compute a damped least squares calculation to optimize a complex illumination system to maximize the irradiance or total power on a receiver. The user can examine several types of interactive output displays including scatter plots, 2D line plots, raster plots in gray scale or pseudo-color, candela plots, 3D surface plots, and contour plots to determine system performance. Encircled flux plots for user-defined circular, elliptical, rectangular, and expanding slit regions can also be created for analysis. Analysis results can be exported and imported in text format for various applications and for post-simulation processing.

Data Exchange Modules

The Data Exchange Modules, which may be individually licensed for use with LightTools, provides import/export connectivity with CAD/CAM programs through industry standard file formats. STEP, SAT, IGES, and CATIA V4 and V5 are the supported formats. Objects such as lightpipes and faceted reflectors created in CAD/CAM programs, when imported into LightTools, are fully raytraceable and can be easily integrated into the model.

Optimization Module

With its Core and Illumination Modules, LightTools provides robust capabilities for creating virtual prototypes and performing illumination simulations. The Optimization Module, which may be individually licensed for use with LightTools, takes the process a step further by searching for the combination of parameters in your system that results in the best performance. By replacing the manual trial-and-error process of trying to find the best solution with an automated optimization process, this can reduce the time required to finalize a design.

Advanced Physics Module

The Advanced Physics Module extends LightTools' optical modeling capabilities for cutting-edge applications. Designers can take advantage of programming extensions to develop custom optical parts and advanced illumination subsystems, such as proprietary polarization components, scatterers, coatings, and other specialty optical materials. The results can be packaged into a portable format and exchanged with your project team, customers, suppliers, and subcontractors.

Imaging Path Module

The Imaging Path Module, which may optionally be licensed for use with LightTools, contains features specifically oriented toward the lens designer. It includes a separate Imaging Path view specifically designed for the creation and analysis of a single sequential surface model for lens design and analysis. It also includes the capability of analyzing the image quality of the lens, such as ray aberration curves and spot diagrams. The Imaging Path view can be used directly in LightTools, or in conjunction with CODE V.

Analysis of the imaging properties of optical systems requires identification of a specific sequence of surfaces along which paraxial and real rays are traced. LightTools automatically ensures that complex systems involving multiple passes through surfaces and beamsplitters are correctly and consistently modeled in both the non-sequential and sequential surface definitions.

LightTools lets you designate any number of surface sequences, called imaging paths, for which paraxial properties and solves, ray aberration curves, spot diagrams, and other quantitative measures of optical performance can be calculated. Paraxial solves can be used to automatically determine or modify the thickness and/or curvature of optical elements in terms of ray heights and angles. Field points can be defined directly or via an x-y graphical view. Reference rays are used for pupil definition. The aperture stop can be defined at any surface.

A single sequentially-defined imaging path cannot contain multiple light paths such as those created by splitters. Instead, a distinct imaging path is created at each split. The definition of these imaging paths can be either automatic via using a "point and shoot" technique where a non-sequential ray is propagated through the system, or user definable via surface-by-surface selection.

 

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