def calcInstrNoiseSq(photParams):
    """
    Combine all of the noise due to intrumentation into one value
    @param [in] photParams is an instantiation of the
    PhotometricParameters class that carries details about the
    photometric response of the telescope.
    @param [out] The noise due to all of these sources added in quadrature
    in ADU counts
    """
    instNoiseSq = (photParams.nexp * photParams.readnoise ** 2 + photParams
        .darkcurrent * photParams.exptime * photParams.nexp + photParams.
        nexp * photParams.othernoise ** 2)
    instNoiseSq = instNoiseSq / (photParams.gain * photParams.gain)
    return instNoiseSq
