You alter how your spells affect illumination.
BENEFIT
Only spells that create areas of light or darkness can be eclipsed spells. If the eclipsed spell creates an area that shines like a torch or raises the light level by one step, you can choose to have the spell lower the illumination level in the affected area by one step, functioning like darkness. If the eclipsed spell creates an area that shines like daylight or raises the light level by two steps, you can choose to have the spell lower the illumination level in the affected area by two steps and create an area of magical darkness, functioning like deeper darkness. If the eclipsed spell lowers the illumination level in the affected area by one step, you can choose to have the spell cause the affected area to glow with normal light, functioning like light. If the eclipsed spell lowers the illumination level in the affected area by two steps, you can choose to have the spell cause the affected area to shed bright light, functioning like daylight.
MP Increase: None (an eclipsed spell does not cost any additional MP to cast.)