(Why does light + light equal darkness?)
A cat's eyesight is 6 times better than a human in lower lighting contitions. When opening (or dilating), a cat's pupils can dilate much faster than yours or mine. They can also dilate three times larger than yours or mine can. This lets in a lot of light, and is one of the reasons cats have their famous ability so see well in low light. They don't see well in total darkness, which is a popular myth, but it is true that their eyes' ability to dilate to such a large degree is part of the reason they have an exceptional ability to see in poorly lit conditions. The one thing everyone seems to notice about a cat's eyes are the pupils. A human pupil is always round, but a cat's pupil can be either round (when it's dilated) or it can shrink in from the sides in stages until it is elliptical. When elliptical, a cat's eyes look like a slit, stretching from top to bottom. This special adaptation allows a cat to squint its eyelids, covering only part of the pupil but not all of it, thus giving it at least some manual control over the amount of light let in. If the pupil was simply reduced to a small circle, closing the eyelids would cover the pupil all together.
light has peak and valleys, just like mountains. if one lights peak meet the other lights valley, they cancel out and u get darkness. peak = max. amplitude, valley = min. amplitude where they meet and cancel = destructive interference
