  Stellar intensity interferometers correlate photons within their coherence
time and could overcome the baseline limitations of existing amplitude
interferometers. Intensity interferometers do not rely on phase coherence of
the optical elements and thus function without high grade optics and light
combining delay lines. However, the coherence time of starlight observed with
realistic optical filter bandwidths (> 0.1 nm) is usually much smaller than the
time resolution of the detection system (> 10 ps), resulting in a greatly
reduced correlation signal. Reaching high signal to noise in a reasonably short
measurement time can be achieved in different ways: either by increasing the
time resolution, which increases the correlation signal height, or by
increasing the photon rate, which decreases statistical uncertainties of the
measurement. We present laboratory measurements employing both approaches and
directly compare them in terms of signal to noise ratio. A high time-resolution
interferometry setup designed for small to intermediate size optical telescopes
and thus lower photon rates (diameters < some meters) is compared to a setup
capable of measuring high photon rates, which is planned to be installed at
Cherenkov telescopes with dish diameters of > 10 m. We use a Xenon lamp as a
common light source simulating starlight. Both setups measure the expected
correlation signal and work at the expected shot-noise limit of statistical
uncertainties for measurement times between 10 min and 23 h. We discuss the
quantitative differences in the measurement results and give an overview of
suitable operation regimes for each of the interferometer concepts.
