Line light

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A line light , also known as a line light , is a bright type of light that is used in particular in line camera inspection systems. As part of this, light with high luminance is projected onto a narrow strip so that line cameras deliver high-contrast images for evaluation even at high web speeds with a high line frequency and the resulting short exposure times . Thanks to the collimated lighting, the line lighting ensures high-contrast results even with large distances.

Line lights

While fluorescent lamps were often used as light sources in the past, these have now been almost entirely replaced by LEDs . LEDs as a light source have a number of advantages over fluorescent tubes, such as a higher light output or the controllability of the output power. This can be implemented both locally (only for partial areas of the luminaire) and for the entire luminaire in a larger dynamic range. Fast triggering of the luminaire is also possible.

In addition to monochrome light colors such as B. red or blue, different shades of white ( color temperatures ) are also available. Illumination in the IR, NIR, SWIR and UV spectrum is also available. The cooling of very powerful lighting is done using water or air. The air or water cooling counteracts overheating of the line lighting.

Areas of application

Line lights are used in image processing systems for quality assurance, defect detection and sorting processes.

Types of lighting

Since different lighting variants are required for quality assurance procedures in industry, a distinction is made between different optical configurations for lighting.

  • Incident light illumination ( bright field )
    • Texture detection - diffuse lighting, if possible from the viewing direction of the camera
    • Excitation in the UV or IR range to determine chemical properties
  • Side lighting ( dark field ) - side lighting at a small angle to detect geometric properties (elevations, holes)
  • Inclined lighting (also reflex or gloss lighting, dark field) - lighting at an inclined angle: This allows the degree of gloss of the surface or the geometric properties (elevations, holes) to be recorded.
  • Transmitted light illumination - illumination through the product mostly to check the product homogeneity (thickness, contamination, cracks, holes, ...) or to determine the product width

literature

  • F. León, M. Heizmann: Forum image processing . Scientific Publishing, Karlsruhe 2010, ISBN 978-3-86644-578-9 .