Le 2026-01-03 à 11:15, William F Pokorny a écrit :
> On 1/2/26 20:44, Kenneth wrote:
>> My original tests used only one 'target' object, so I tested again 
>> using two,
>> and you're right: A changed multiplier value does work now (for both 
>> targets),
>> even when 'count' is used in the global photons block. This little 
>> 'switch' in
>> behavior is undocumented, as far as I can tell.
>>
>> However: Given two (or more) 'target' objects in a scene, the photon 
>> behavior
>> for each can be unexpectedly different, depending on whether 'count' vs.
>> 'spacing' is used:
>>
>> A) With 'count':
>>       If two targets both use a value of 1.0 (or simply 'on'), the 
>> 'count' of
>>       photons is*split up evenly* between the two; each target gets 
>> half the
>>       count. But if one target uses 1.0 and the other 0.2, the 0.2 
>> target*robs*
>>       photons from the 1.0 target, with the resulting visual caustic 
>> effect on
>>       surfaces looking different from each one. But the total photon
>>      'count' remains the same.
>>
>> B) With 'spacing':
>>       Each target is*independent*-- they each respond to their individual
>>       spacing-multiplier values, no 'robbing' of photons...which means 
>> the total
>>       NUMBER of photons can increase, to suit the situation. This would
>>       produce a more logical and visually realistic result than 'count'.
> 
> Re: (A) Interesting & news to me. I thought the count applied 
> independently to each target. Thanks for digging into the behavior!
> 
> Bill P.

When you use count, the count value is the total number of photons to be 
shot, distributed between all targets and all lights. The area, or 
angular size, of the targets also play a role. A big target will tend to 
get more photons than a small target next to it.

The photon shooting always try to keep the photon density constant 
between all targets.

count 1 000 000
two lights and two targets of roughly the same size, and each light will 
shoot about 250 000 photons at each target.

Have three targets, and you shoot about 166 666 photons per light at 
each target.

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