When working with long strips of NeoPixel, it is quite useful to chunk them into ranges and apply independent colors and animations to them. The range allows to create a new NeoPixel strip instance over a subset of the pixels.

// mount an external Neopixel strip on pin A1 with 24 RGB pixels
let strip = light.createStrip(pins.A1, 24);

// create 2 ranges for each half of the strip
let head = strip.range(0, 12);
let tail = strip.range(12, 12);

Once you have your rangers defined, you can easily apply colors and animation without worrying about complicated index computations.

// turn on 1 pixel on each range
head.setPixelColor(0, Colors.Blue)
tail.setPixelColor(11, Colors.Red)

The example below create 2 ranges and moves the pixels on opposite directions on each of them.