#include <FastLED.h>

const int numLeds = 30;
const int ledStripPin = 6;

CRGB leds[numLeds];

void setup() {
  FastLED.addLeds<NEOPIXEL, ledStripPin>(leds, numLeds);
  FastLED.setMaxPowerInVoltsAndMilliamps(5, 400);
  FastLED.setBrightness(8);
}

void loop() {
  for (int light=0; light<30; light+=2) {
    leds[light] = CRGB::Red;
  }
  for (int light=1; light<30; light+=2) {
    leds[light] = CRGB::Blue;
  }
  FastLED.show();
  delay(500);
  for (int light=1; light<30; light+=2) {
    leds[light] = CRGB::Red;
  }
  for (int light=0; light<30; light+=2) {
    leds[light] = CRGB::Blue;
  }
  FastLED.show();
  delay(500);
}