For certain types of design, ray tracing is not desirable but demanded. For example, in the design of optical systems (lens, mirrors, and other components), jewelry design, lighting fixtures, and lamp design. In addition to such physical designs, there is a field of ray tracing for wave and field design in radio and acoustics. In these examples, the design, and resultant images and data must be absolutely physically accurate and photorealistic.
Rendering and ray tracing software comes in various packages as stand-alone programs, integrated with a 3D modeler, or as a plug-in. A wide range of professions use photorealistic renderings such as architects, product designers, and engineers. Hollywood uses rendering in making CGI blockbusters; video game developers use it for cars and robots, and scientists use it for optics and subterranean exploration. Physically accurate renderings help doctors and radiologists find things that aren't easily revealed on a simple x-ray or MRI layer.
The use of ray tracing begins with the proposal for a product, bridge, automobile, movie or packaging concept. Used during design and pre-production in virtual prototyping, pre-viz, and concept sign off and, of course, it’s used extensively in marketing.