1. An excessive fear of daylight or of sunlight: Human manifestations of phengophobia involve secluding themselves in curtained rooms where the brilliance of the sun cannot enter and only allowing illumination by artificial lambency. Usually the individual can go out at night and move around in greater comfort than during solar time. 2. In biology, intolerance of luminosity: Some creatures have a natural phengophobia, including certain plants and animals, because they cannot exist in bright fulgence.