Spectroscopy in the optical, UV as well as IR range is a widely used method for analysis and quality control. Due to the individual spectral characteristics of materials, product compositions and properties can be analyzed with the highest precision. Using light guides, this method can also be used in inaccessible places in production processes. In extreme environments such as high temperatures, dirt and humidity, light guides offer the possibility of placing sensitive analytical equipment far away from the measuring point in protected environments.