What happens at the “edges” of the visible light spectrum?

Question

We can “see” light between 380 and 700 nanometers, but what happens at the egde and just after that? I mean, when we approach the limit like 699-700-701-705…
Does it turn completely dark/invisible/something else immediately or is there some kind of gradual change?
Is it the same on both ends?

In: 17

Answer 1

https://i.stack.imgur.com/vxjpm.png

Those are the sensitivity curves of the cones in our eyes. As you can see, they indeed just trial off.

It’s telling that not all people have equally sensitive cones, so some people can see a bit further into red and violet than others in the right conditions, like in a perfectly dark room. Because the light would be very dim in their eyes, even if the source is “bright” (energy wise).