Multiple 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. 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 3-D location. Traditional programs demand that the engineer specify which optical surfaces the light will hit, and in what order (sequential ray tracing). However, LightTools default mode supports non-sequential ray tracing in which 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.

Because of the nature of optical design, LightTools accuracy is much greater than software used for mechanical design. When designing or machining a mechanical part, accuracy within 0.02 mm (0.0008 in.) 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 formulae that facilitate the maintaining of surface shape, position, and intersection to optical accuracy for all calculations. This accuracy ensures that the model performs as the real system will.

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 the software 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 of the optical system, which is useful for design verification, visualization, and communication.

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

•	Core Module (required) — essential modeling visualization and ray tracing capabilities
•	Illumination Module (optional) — adds sources, receivers, and analysis features for illumination
•	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 (STEP, SAT, and IGES).

Industry applications of the software include projection systems, flat-panel displays, interior vehicle lighting, segmented mirrors, sign lighting, machine vision systems, and medical optics illumination.