The visual clarity of a lighting environment is significantly affected by changing the general color rendering index (Ra) of its illumination. This effect has been studied by a number of researchers, but the cause of this effect has not been thoroughly studied. In order to clarify this, the mutual relations between visual clarity, lightness perception, and feeling of contrast are analyzed by using object colors under illuminations with various Ra values. The results obtained are as follows. (1) The visual clarity of a lighting environment is different from the lightness perception of the object colors in the environment. (2) The change in visual clarity of a lighting environment is highly correlated to a feeling of contrast between object colors under the illumination. (3) The effect of visual clarity is estimated effectively by assessing the feeling of contrast using a specially selected four-color combination. (4) The illuminance for equal visual clarity for any illumination is predicted by the equality of feeling of contrast under the same illumination specified by the gamut area made by the component colors of the four-color combination in a brightness and colorfulness space. (5) The effect of visual clarity under various illuminations cannot be predicted by using their Ra values.