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Q&A: How many rays should I trace?

Question
How many rays should I trace?

Synopsis
How many rays should I trace?

Solution
There is no general answer to how many rays should be traced, but there is a
useful feature for assessing the uncertainty. Please select Raytrace/Raytrace
Options, and note that there is a Random Seed setting, usually set to the
default value of 1.

There are numerous calculations performed in a TracePro ray trace and many of
them, like the direction of a scatter ray or the position on a surface that a
ray is emitted from a Surface Source, involve the use of a Random Number
Generator algorithm within TracePro.

If TracePro simply used the Random Number Generator alone, then you could
click Trace Rays in TracePro, view the analysis results, then click Trace rays
again and get a completely different set of rays to trace. If enough rays are
traced, all ray traces would converge to a single analysis result.

The Random Seed feature of TracePro is what allows you to trace rays, today,
next week, and next month, and get the exact same set of rays to trace. This
seed is used to start the Random Number Generator in the same place each time.

This is a useful behavior, but it can also lead to a false sense of security
that the analysis result is absolutely correct.

By performing additional ray traces with the Random Seed set to 2, 3, 4, …
100000, you can assess if the variation in these ray sets is beyond the comfort
zone of your analysis. If so, the resolution is to trace more rays.

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