Thanks for checking, Nathan.
The file was V5 before, I imported it into V6.4
Hence, it was never opened in V6.3
As I said before (in the bug report about zombie lights), these behaviors seem hard to reproduce and light system seems quite shakey to me. If I change a few parameters forth and back (exactly), I seem to end up with completely different results. Barely visible light vs brutally overexposed after closing and reopening a file.
Trying to setup / strip down a test file for you, I see a lot of inconsitent behavior, though directly after opening the file everything seems to work fine.
I might have narrowed it down a bit:
While in Raytraced, any changes made to the light intensity are ignored. With each change of the value (hitting enter/tab), Cycles will start counting render passes from 0 (making the user believe that the changes got applied), while the changed settings are in fact not applied. Only when you change to another display mode and back, the changes will be applied.
Same is true for light color, layer visibility (of layers with light objects), …
Hope this is a resonably clear description.
LightsBug_FSP_01.3dm (733.6 KB)