Large or Diffuse Light Sources

ආලොක කිරණ අපසාරී හෙවත් විසිරී යයි, සමාන්තර නොවේ.
හොඳින් පෙනෙන දැකුම් වෘත්තයක් තිබේ.
එක මත වැටෙන ද්වි සෙවනැලි සෑදේ.
එයට සූර්ය ආලෝකය හෝ එහි පරාවර්ථන බලපෑම් ඇතිවිය හැක. සංකීර්ණ සෙවනැලි ඇතිකරයි.
තද අඳුරු සෙවනැලි අරටුවක් තිබේ.
මෙහිදී ප්‍රභවය සංකීර්ණ විසුරුම් ජනේලයක් සාදයි.
විසුරුම් ජනේලයේ වටය හා අඳුරු අරටුව ලබා ගැනීමට ජ්‍යාමිතිය භාවිතා කළ හැක.

මේ ජනෙල් කවුළුවකින් වැටෙන ආලෝකයෙන් ජනිත වන සෙවනැල්ලකි.
A in the window and points, a1 and a2 on cylinder.
A, a1, a2 cast two shadow points, s1 and s2, on the horizontal surface.
Point A is the light vanishing point
point C is on the horizontal plane directly below A
C is the vertical shadow vanishing point (svp [vertical]).

The penumbra

When all points in the window are mapped in this way, the result is a large diffuse area of overlapping shadows. This composite shadow is lightest at the edges and at the extreme end from the cylinder, which receives some direct light from some parts of the window.

The umbra

The darkest at the center just behind the base of the cylinder is the umbra. It receives no direct light from any part of the window. All diffuse shadows have a penumbra, but they only have an umbra if the shadow casting object is close enough to the shadow receiving surface to completely block all light from all parts of the light source. The umbra is uniform in darkness and the shadow lightens continuously between the edge of the umbra and the edge of the penumbra.

All diffuse cast shadows can be solved in a similar way, first by plotting the extreme outside edges of the shadow from the extreme top, side and bottom points of the large light source, which will show the boundaries of the penumbra and umbra, then gradating the difference between the umbral and penumbral values from the edge of the umbra out to the edge of the penumbra.

The amount of lightness contrast between the diffuse shadow and the illuminated part of the horizontal surface depends on the total amount of light coming from the diffuse light source (the window), the proportion of light coming from other sources in the room, including reflected light from the walls and ceilings, and the light adaptation of the eye.

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