Generally, people experience psychological healing when they encounter illumination from candlelight or fireflies. Such slowly changing light can be regarded as qualitative psychological healing. However, the relation between space and human psychology is not represented quantitatively in illuminated environments with slowly changing light. In this study, 12 simulations each containing four types of illuminance transition patterns and three time periods were carried out in a custom built experimental space. The simulations were prepared from 12 graphs of waveforms from prior experiment results. On the graphs, the vertical axis represented time and the horizontal axis represented luminance. The waveforms consisted of square waves, triangle waves, sawtooth waves, and reverse-sawtooth waves, each containing three different time periods of illumination. Each wave had an illuminated environment and brightness transition from lux to 500 lux and from 500 lux to lux. The square waves generated short transitions; the triangle waves generated long transitions; and the sawtooth waves generated alternating long and short transitions. Thirty participants took part in the experiment at the custom built experimental space. They evaluated their psychological responses to the effects of the transitional illumination by answering 16 questions, each containing seven possible levels of response. Results demonstrated that triangle waves had an affirmative effect on relaxation, comfort, naturalness, safety, calmness, and healing. In detail, these results indicated that a brightness transition from lux to 500 lux in 20 seconds and a brightness transition from 500 lux to lux in 20 seconds had a positive effect on psychological healing. These results suggest that a smooth and slow transition of light and darkness, as well as a slow transition of brightness, reduced the participant’s mental burden. These findings propose that a smooth and slow transition of light and darkness has an affirmative effect on healing. Therefore, these outcomes suggest illuminated environments with slow and smooth transitional illumination have an affirmative effect on healing. Based on these findings, in order for psychological healing to occur it is necessary to manage the slow and smooth lighting transitions of an illuminated environment.