hi,
Andy, look at datasheet. At node Peak Current it should be noted at which duty cycle and frequence it is required.

For example, here I use Kingbright TBA23. They say that peak current is 140...160mA with next condition: 1/10 Duty Cycle, 0.1ms Pulse Width. Thus if pulse width is longer then current must be decreased. From other side, if frequence is highter, you should not increase current because it may destroy LEDs or wires inside part (there is maximum limit depend on physical realization of it). So you may set maximum current only if pulses` frequence is at indicated value or above (of course, with correct duty cycle). In my application I use 500Hz.
Another question is duty cycle. I cannot understand why they have indicated 1/10 while the part has only 8 columns and so it should be 1/8 logically. Why? I dunno.

Regards,
Oleg