  Ensembles of nitrogen-vacancy (NV) center spins in diamond offer a robust,
precise and accurate magnetic sensor. As their applications move beyond the
laboratory, practical considerations including size, complexity, and power
consumption become important. Here, we compare two commonly-employed NV
magnetometry techniques -- continuous-wave (CW) vs pulsed magnetic resonance --
in a scenario limited by total available optical power. We develop a consistent
theoretical model for the magnetic sensitivity of each protocol that
incorporates NV photophysics - in particular, including the incomplete spin
polarization associated with limited optical power; after comparing the models'
behaviour to experiments, we use them to predict the relative DC sensitivity of
CW versus pulsed operation for an optical-power-limited, shot-noise-limited NV
ensemble magnetometer. We find a $\sim 2-3 \times$ gain in sensitivity for
pulsed operation, which is significantly smaller than seen in power-unlimited,
single-NV experiments. Our results provide a resource for practical sensor
development, informing protocol choice and identifying optimal operation
regimes when optical power is constrained.
