It's quite hard to find a definition of Instrumented Environments online. Here are two.
Instrumented environments provide a sandbox in which ubiquitous computing scenarios can be investigated. Instruments and devices embedded in the environment give things and places the power to display or sense information. They provide the connecting points between the physical world, in which they are located, and the virtual world to which they are connected. In this sense, the instrumentation of an environment augments it without the use of classical AR tools, such as projection or head-worn displays.
For my diploma thesis I tried to give a more pragmatic definition:
Instrumented Environments (IE) are an instantiation of Ubiquitous Computing, focusing on human-computer interaction with physical environments, e.g. a room or a desk. In an instrumented environment the user can view, input or modify data using different interaction modalities (gestures, tangible user interfaces) and different display devices (mobile devices, tablet PCs, wall-sized displays, steerable projectors). Instrumented environments use sensor data to support explicit interaction.
Wimmer: "Capacitive Sensing for Instrumented Environments", Diploma Thesis, 2006