uC -> wire -> LED in metal enclosure. ESD/EMI protection
Neither LEDs nor microcontroller outputs have exposed ESD-sensitive MOSFET gates. If your LED box contains MOSFET drivers then you may need protection there; there are dedicated chips strictly for ESD protection, or you could examine discrete logic chips where the manufacturer has designed the chip for increased ESD protection (e.g. Fairchild Semiconductor's 74HC/HCTxx series)