#include <FastLED.h>
    #define NUM_LEDS 5120
    #define DATA_PIN 2
        CRGB leds[NUM_LEDS];
           void setup() { 
       FastLED.addLeds<NEOPIXEL, DATA_PIN>(leds, NUM_LEDS);
   }
       void loop() {
        for(int dot = 2500; dot < NUM_LEDS; dot++) { 
            leds[dot] = CRGB::Blue;
            FastLED.show();
            // clear this led for the next time around the loop
            leds[dot] = CRGB::Black;
            delay(10);
        }
    }