import math


def base_exponential_non_linearity(n):
    """
    Returns the base exponential non linearity :math:`n`.

    Parameters
    ----------
    n : numeric
        Function of the luminance factor of the background :math:`n`.

    Returns
    -------
    numeric
        Base exponential non linearity :math:`z`.

    Examples
    --------
    >>> base_exponential_non_linearity(0.2)  # doctest: +ELLIPSIS
    1.9272135...
    """

    z = 1.48 + math.sqrt(n)
    return z