In designing a circuit, the current through each LED must not exceed the absolute maximum rating specified for each LED. In the meanwhile, resistors for protection should be applied, otherwise sight voltage shift will cause big current change, burn out may happen.

It is recommended to use circuit A while regulates the current flowing though each LED rather than circuit B. When driving LEDs with a constant voltage in circuit B, the current through the LEDs may vary due to the variation in Forward voltage (VF) of the LED. In the worst case, some LED may be subjected to current that exceed absolute maximum rating.

Thermal design is paramount importance because heat generation may result in the characteristics decline, such as brightness decreased, color changed and so on. You should consider the heat generation of the LEDs when making the PCB design.

Page address: http://www.verypixel.com/blog/Suggestions_for_LED_Display_PCB_design.html