# How does transition from violet visible light to invisible ultraviolet look like?

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?

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.

• I am wondering is there such sources that can smoothly transit radiation frequency from visible to invisible🤔 Jan 18, 2022 at 10:35
• Some lasers can do that, yes.
– noah
Jan 18, 2022 at 10:49
• Lasers? Lasers, on the contrary, radiate almost monochromatic light. Maybe You meant due to temperature changes? What are that lasers? Jan 18, 2022 at 11:24
• Yes, when you asked about "varying the frequency" I assumed (and noted in my answer) we are talking about monochromatic light. Some laser setups emit (almost) a single wavelength, but you get to choose which one it is smoothly over some range. They are typically called tunable lasers.
– noah
Jan 18, 2022 at 11:41
• First time see it, very interesting Jan 18, 2022 at 11:49