  We have measured and compared the response of hybrid NbTiN-Al Microwave
Kinetic Inductance Detectors (MKIDs) to changes in bath temperature and
illumination by sub-mm radiation. We show that these two stimulants have an
equivalent effect on the resonance feature of hybrid MKIDs. We determine an
electrical NEP from the measured temperature responsivity, quasiparticle
recombination time, superconducting transition temperature and noise spectrum,
all of which can be measured in a dark environment. For the two hybrid NbTiN-Al
MKIDs studied in detail the electrical NEP is within a factor of two of the
optical NEP, which is measured directly using a blackbody source.
