Low-fidelity prototypes are early sketches of the initial design idea. In web and software design, these are often static wireframes that range from ideas sketched by hand on paper, basic slides created in software such as PowerPoint, or wireframes created in prototyping software such as Axure.
The rudimentary nature of these artifacts is reflect by the term, "low-fidelity". The key value of such artifacts is that they are inexpensive--it is possible to create many variations and explorations of the products relatively quickly, and the means of creation are inexpensive as well.
The preceding picture shows examples of low-fidelity prototypes that were created to explore and test the design of physical and digital products. The thinking is that raw design ideas should go through iterations in a raw state, before moving to a more detailed, refined prototype.
It is possible to put these prototypes in front of potential users and engage in research that involves aspects of macro usability, such as the prioritization of desirable features and functionality, layout, position of buttons, and other high-level design aspects, that are not directly dependent on the experience itself. The focus is on what users need or want to do with the products.
Many designers believe strongly in sharing low-fidelity designs that are executed only in grayscale or black and white colors. The theory behind this approach is that adding actual color to such prototypes confuses stakeholders and testers, who would conflate the prototype with the final design and shift their responses to immaterial topics, such as the nuances of the colors used in the prototype.
Grayscale prototypes make it easier to concentrate on essential aspects of the experience, such as navigation and information architecture. Only after the designer has validated that an approach is successful, it makes sense to transition to much more detailed high-fidelity prototyping. The preceding picture shows the prototype of the same page as low-fidelity grayscale wireframe (A), and a highly detailed version (B).
The following picture shows various examples of high-fidelity prototypes. The term points to the prototype's level of detail and general resemblance to the final product. In web and software design, participants in usability testing experience a look and feel that closely approximates the actual experience--elements on the screen are clickable while content and data elements are simulated to respond to tester actions. The results are always reliable and accurate, and the effectiveness of such prototyping is so compelling that some designers argue for starting with high-fidelity prototypes from the get-go, and forego the use of low-fidelity prototypes altogether.
The benefits are clear, as mentioned previously, but so are the risks that the time and effort invested in a complex, detailed prototype too early in the process, would tie the designer to a sub-optimal concept. Cheap, simple prototypes are easy to scrap, while expensive ones, not so much. The agility and flexibility of prototyping as a means of iteratively and frequently testing and adjusting the design must be preserved.
The timing of testing is critical, and the main concern about testing high-fidelity prototypes is that by the time such prototypes are tested and results compiled, it is often too late for the engineering team to make any significant changes to the product without negatively impacting costs and the target release date.