By increasing the frequency of electromagnetic wave in visible range, human eye sees it as a color change.
But how human eye will see transition after violet wavelength to ultraviolet? As far as I understand ultraviolet (at least middle and far ranges) is invisible for eye.
So if imagine some source that can smoothly change frequency of the radiation from violet to (far) ultraviolet, how human will see it?
Will it just smoothly disappear?
Best Answer
The sensitivity of your cone cells (the ones that see color) varies with frequency, as shown in this nice graph from Wikipedia.
If you had a monochromatic light source of constant intensity, but could smoothly vary the frequency, it would appear to your eyes as becoming brighter and dimmer across different frequencies.
On the far left of the graph you can see that the sensitivity of the S cones smoothly (but quite steeply) goes to zero. This is exactly the brightness you would see if you were to tune your light source from violet to ultraviolet, i.e. you would observe smooth dimming of the light until it is gone.