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Illumination: Light propagation and geometry

The quality of illumination can vary depending on the object material and how structured the light is. Different illuminators are available delivering light ranging from structured to diffuse. Mirrors or lenses can be used to focus the light in one direction or scatter the light such that it reaches the object from all directions (diffuse).

The term light propagation describes the manner in which light strikes an object. We will be concerned with the effects of collimation, structure, focus and diffusion. In the diagram below, these have been arranged together on a scale that has structured laser light at one extreme, and diffuse light at the other. In this context it should be noted that the terms diffuse and even when related to illumination, are not explicitly the same.


  • Structured
    Coherent laser light where the waves/photons share the same phase

  • Collimated
    Collimated on-axis illumination, where the rays of the light are all parallel

  • Focused
    Focused laser light, or a line light that is focused onto the surface of a web

  • Direct
    LED light, where the light from the array has a direct path to the target

  • Diffuse
    LED light, where the light from the array passes through a diffusing material

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