Development and evaluation of a new line illumination for hyperspectral imaging systems for industrial applications

Hyperspectral line-scan systems are widely employed in industrial sorting applications to distinguish materials based on subtle spectral characteristics, or spectral fingerprints, that are imperceptible to the human eye. Common applications include contaminant detection in food processing and the separation of different plastic types. These systems are well suited for high-throughput inspection due to their ability to capture spatial and spectral information line by line. In such systems, a narrow line across the sample, perpendicular to the direction of relative motion, is projected onto an imaging spectrograph, where the spectral information of each spatial pixel is dispersed along the second axis of a two-dimensional detector. Consequently, only a line-shaped region of the sample requires illumination. Conventional illumination configurations employ multiple halogen spotlights that produce overlapping elliptical illumination areas. While this approach ensures coverage of the region of interest, it results in non-uniform intensity distribution along the scan line and illuminates a larger area than necessary. In this work, we propose an alternative illumination concept utilizing readily available automotive H7 halogen headlight bulbs in combination with an elliptical reflector and a lens array. The performance of the proposed system is compared to that of conventional halogen spot illumination in terms of intensity uniformity and spectral performance.