def METHOD_NAME(
    sd: SpectralDistribution, lef: SpectralDistribution | None = None
) -> float:
    """
    Return the *luminous efficacy* in :math:`lm\\cdot W^{-1}` of given
    spectral distribution using given luminous efficiency function.
    Parameters
    ----------
    sd
        test spectral distribution
    lef
        :math:`V(\\lambda)` luminous efficiency function, default to the
        *CIE 1924 Photopic Standard Observer*.
    Returns
    -------
    :class:`float`
        Luminous efficacy in :math:`lm\\cdot W^{-1}`.
    References
    ----------
    :cite:`Wikipedia2005c`
    Examples
    --------
    >>> from colour import SDS_LIGHT_SOURCES
    >>> sd = SDS_LIGHT_SOURCES["Neodimium Incandescent"]
    >>> luminous_efficacy(sd)  # doctest: +ELLIPSIS
    136.2170803...
    """
    efficacy = CONSTANT_K_M * luminous_efficiency(sd, lef)
    return as_float_scalar(efficacy)