We present measurements of the V- and I-band magnitudes of red clump stars in 15 nearby galaxies obtained from recently published homogeneous Hubble Space Telescope photometry. Supplementing these results with similar data for another eight galaxies available in the literature, the populational effects on the V- and I-band magnitudes of red clump stars were investigated. Comparing red clump magnitudes with the I-band magnitude of the tip of the red giant branch in a total sample of 23 galaxies possessing very different environments, we demonstrate that population effects strongly affect both the V- and I-band magnitude of red clump stars in a complex way. Our empirical results basically confirm the theoretical results of Girardi & Salaris, and show that optical (V – I) photometry of red clump stars is not an accurate method for the determination of distances to nearby galaxies at the present moment, as long as the population effects are not better calibrated, both empirically and theoretically. Near-infrared photometry is a much better way to measure galaxy distances with red clump stars given its smaller sensitivity to population effects.
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