def convertWavelength(wavelength) -> str:
    """
    Convert wavelength into string in nano meter.

    Parameters
    ----------
    wavelength : str, int, float
        Wavelength in nano meters or micro meters

    Returns
    -------
    str
        Wavelength as string

    Raises
    ------
    ValueError
        If wavelegnth between 5 and 200

    """
    # micro meter
    if float(wavelength) < 5.0:
        return str(int(float(wavelength)*1000))

    # nano meter
    if int(wavelength) > 200:
        return str(int(wavelength))

    # invalid wavelength
    raise ValueError("Warning: Could not convert wavelength.")