1. An excessive avoidance of light: Mrs. Jones, suffering from photophobia, had light-coloured eyes which were very sensitive to the brilliance of the sun and caused her much discomfort and pain.
2. In botany, the tendency to thrive in reduced light: Moss, which exhibits photophobia, grows in moist, shady areas and won't survive well in sunlight!
3. Intolerance of full light: Photophobia is indicated by troglobites, animals which spend their entire lives in caves and having adapted a loss of body pigmentation, a loss of sight, and slow metabolic activity.