This project will develop and qualify a new assistive technology to aid persons who are blind. The Indoor/Outdoor Navigation System (IONS) will provide guidance, wayfinding and environmental awareness information. Currently Sendero Group LLC offers the BlindNote/VoiceNote PDA with GPS capability for outdoor locating and wayfinding. Indoors, where GPS does not function well, the system uses an inertial guidance system that can be prone to accumulated location error. This project will demonstrate the concept of using inexpensive illumination-based Talking Lights optical locators to reduce or eliminate this location error and make very precise GPS-like guidance possible indoors. IOLS will provide personalized cues and guidance, allowing users who are blind to follow predetermined routes or create and share their own routes in buildings. Talking Lights optical transmitters use modified, non-flickering room illumination to provide location and can be very inexpensive to implement and maintain. Application areas will include museums, malls, hospitals, schools, retail stores, trade shows, transportation facilities and other places where the blind travel. IONS will be demonstrated and evaluated with blind travelers and its assistive capability quantitatively measured. Hardware devebped will include enhanced optical receivers to provide precise location information to the BrailleNote/VoiceNote PDA. Software developed will allow Talking Lights locators to provide GPS-like locator information indoors and permit the input of location to the PDA, updating of location and elimination of errors.