Change direction of the leds

Other Hardware LEDs and Multiplexing
9

In order to turn off an LED you set the colour to Black.

So, to set the first 10 lights on each strip to red.

for ( byte i = 0; i < NUM_LEDS; i++ ) {
    If (i > 9) {
        ledstrip_1[i] = CRGB::Black;
        ledstrip_2[i] = CRGB::Black;
        ledstrip_3[i] = CRGB::Black;
        ledstrip_4[i] = CRGB::Black;
        FastLED.delay(1000);
        Coninue;
   }

    ledstrip_1[i] = CRGB::Red;
    ledstrip_2[i] = CRGB::Red;
    ledstrip_3[i] = CRGB::Red;
    ledstrip_4[i] = CRGB::Red;
    FastLED.delay(1000);

  }