Photometric transit depth vs. apparent stellar m_V magnitude for transiting exoplanet systems. Symbol diameters are proportional to the duration of transit. The demanding observational requirements limit current studies to the brightest stars with the largest planets, i.e., HD 209458 and HD 189733A. Data for systems with reasonably well-determined properties were taken from the Exoplanet Orbit Database (2017) and Han et al. (2014).