def reflection(n1: float, n2: float) -> float:
    """Returns power reflection at the interface
    of two refractive index materials.

    Args:
        n1: Refractive index of material 1.
        n2: Refractive index of material 2.

    Returns:
        float: The percentage of reflected power.
    """
    r = abs((n1 - n2) / (n1 + n2)) ** 2
    return r