The perceptual gloss space defined in Pellacini et al. [9] could be used for quality control applications to bring similar benefits as seen in color with the use of CIELAB. However, a distance metric to relate all the dimensions in the space does not exist, and the space was only validated with the materials used to define the space. The current space's distance metric does not allow relating differences in lightness to the other dimensions: contrast gloss and distinctness of image gloss. The lightness perception uniformity of the space was first evaluated in a psychophysical study, where the observers' lightness discrimination was found to decrease as lightness increased. A function was derived to model the lightness perception observed and it was included into the distance metric of the space. The space uniformity around sixteen positions in the gloss space was evaluated in a second psychophysical study to assess the overall space uniformity. The space was found to be perceptually non-uniform outside the samples used when the space was created. Also, an improved gloss difference equation that takes into account the non-uniformity of the space is presented, showing a statistical significant improvement over the current gloss difference equation of the space and reducing the STRESS value from 39.76 to 22.96.