In this study we investigated the relation between the level of illumination and the perception of objects in a realistic visual environment by visually impaired subjects. Not fully surprising, we found that object perception improved when we increased light levels. It should be noticed that substantial improvements could often be observed at light levels that were considerably higher than normal. Furthermore, we found that integrated contrast sensitivity is a suitable summary measure for the contrast sensitivity function. It correlates very well with the number of objects that were detected and recognized at different light levels. It also proved to be a much better predictor of visual performance than visual acuity. We infer from this that when we try to create the best possible illumination for orientation and day-to-day purposes we should optimize a person’s contrast sensitivity. In order to predict perceptual abilities in real life, it is of paramount importance to have a clear description of someone’s contrast sensitivity.