anarchy2465:
There is no resistor between the 74HC595 and the LEDs. ... The LEDs are connected by a common cathode and all the current is sunk by an IRFS630B MOSFET (200V, 9A).
I was working with LEDs yesterday, 32 of them:
I was thinking "how can I save soldering 32 resistors?" and thought of doing what you did - a constant current sink. But I decided against it on the grounds that the current being sunk would be shared, and the more LEDs that lit up, the more current would need to be sunk, and that the results wouldn't be even. Your report appears to confirm that.
Perhaps you can clarify how you are managing the current. In the absence of resistors are you going for a constant current sink, or relying on PWM to limit it?