Sunlight is quite bright and looking directly at the Sun is painful to the eyes. Looking directly at the Sun when it is high in the sky causes temporary bleaching of the photosensitive pigments in the retina, which makes phosphene visual artifacts and temporary partial blindness. Direct viewing of the Sun with the naked eye delivers about 4 milliwatts of sunlight to the retina that is in the solar image, heating it up and potentially (though not normally) damaging it. Brief viewing of the direct Sun with the naked eye is unpleasant but generally safe. Long-term exposure of the eyes to direct sunlight contributes to the normal UV-induced yellowing of the lens and cornea over periods of decades, and could play a part in the formation of cataracts.