| In relation to the distances between the light source and the illuminated object light rays can be considered to be of three types: converging towards the illuminated object, diverging from the illuminated object or infinite. In the latter case the light rays intersect at a point at infinity (improper point). The choice of the type of source to be taken to determine which zone is light and which is in the shadow of an illuminated object is arbitrary and depends on the size of the object as well as illuminating and illuminated by the relative distance between the object and the light source. Thus, for example, the source of the light rays of the sun, which is 150 million kilometers from Earth, can be regarded as improper point with respect to ground, but not with respect to the planetary system. Consider the light rays coming from a point improper means that these are parallel to each other and the projection, on a plane, of the apparent contour of the illuminated object follows a parallel projection (orthogonal projection). |
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