system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Moving things in the dark are lower ''fps"?

Whenever I look at something that has a spotlight or a focused bit of light shining on it for example someone's hand, then they move it really fast. It seems as if their hand is moving in "lower fps'' than usual.   
I'm not sure in what other way to put it, I've only recently noticed it.
gpt
Your eyes have two types of light sensitive cells called photoreceptors.

One type, cone photoreceptors, have 3 configurations that make up our color vision. They can repeatably fire and are very concentrated in the center of your vision. The downside is that they require a lot of light to fire so they're used for medium to bright environments.

The other type, rod photoreceptor, are extremely sensitive to light but reload very slowly. They are concentrated in the peripheral of your field of view. Rod photoreceptors are useful when it's dark or dim.

In dark environments, your cones don't have enough light to fire so your rods do most of the work. Although rods are very sensitive to light, they recover slowly, giving you the feel that things have low FPS or blur more. You'll also notice you can't sense color very easily. Rods only report black and white so your vision is mostly gray.