Over-illumination is when there is too much light in a room or space. When it is too bright, it can make it difficult to see things clearly, and it can also cause discomfort in the eyes. It can happen when there are too many lights turned on, or if the lights are too bright for the room they are in. Think of it like being in the sun on a hot day without any sunglasses or a hat, except for your eyes. It can be unpleasant and make it hard to look at anything.