#include <FastLED.h>

#define NUM_LEDS 120
#define LED_PIN 3
#define POT_PIN A0

CRGB leds [NUM_LEDS];

uint8_t hue = 0; 

void setup() {
  FastLED.addLeds<WS2812B, LED_PIN, GRB> (leds, NUM_LEDS);
  FastLED.setBrightness(50);
 
}

void loop() {
for(int i = 0;i < NUM_LEDS; i++){
  leds[i] = CHSV(hue, 255,255); // also: leds[i] = CHSV(hue + (i * 5), 255,255);
}
 EVERY_N_MILLISECONDS (15){
  hue++;
}
FastLED.show();
}