<p dir="ltr">This is already done to a certain extent by cycles automatically.</p>
<div class="gmail_quote">On Feb 3, 2015 4:19 PM, "Zauber Paracelsus" <<a href="mailto:zauber@gridmail.org">zauber@gridmail.org</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Would it be possible, through a new lamp setting, to support<br>
distance-based culling of lamps? The basic idea is that lamps would not<br>
be sampled if they are far enough away from the area being sampled,<br>
thereby cutting down on rendering time.<br>
<br>
This can already be done to a degree by using nodes via the Ray Length<br>
output of the Light Path node, and I find that in complex scenes with<br>
numerous surfaces and several lamps over a large area, it can reduce<br>
rendering times by roughly half.<br>
<br>
However, there are two flaws with this approach:<br>
1) Ray Length only measures the length of the current ray, meaning it<br>
could still be sampled despite being a greater distance away.<br>
2) Ray Length is supplied after a bounce is calculated (I think),<br>
meaning it would not be fully sufficient to stop the lamp from being<br>
sampled.<br>
<br>
If distance culling for lamps is supported directly within blender,<br>
however, then it would perhaps unlock larger performance gains because<br>
it would stop the lamp from being sampled before any bounces are calculated.<br>
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</blockquote></div>