Either a UV laser/lamp, or you need a broadband light source, like sunlight, and a filter/monochromator of some kind (either using a prism or a diffraction grating, or a bandpass filter). You could find something that only reflected UV, yes, but only if you had a source that emitted UV in the first place. Odds are most people don't want UV emitters in a screen they look at 6 hours a day.
The point is that you need a source which contains the wavelength of interest. Monitor leds are red/green/blue and don't emit violet photons. 405nm is usually somewhat visible, if a bit blurry. Blue leds are usually Gallium Nitride based which produces more like 450nm.
I see "spectral violet" and "UV" in two different comments. I have the understanding that "ultraviolet" is past violet and outside the visible spectrum. So now I have questions...
Do spectral violet and ultraviolet differ? In what way? If something isn't visible, why does it matter?
A UV lamp will emit a range of frequencies, and one the lower frequency side of that distribution will be some spectral violet, along with a bunch of UV you can't see.
Spectral violet and ultraviolet are just two ranges on the continuous frequency spectrum, so they differ in frequency.
Yes, ultraviolet is technically outside the visible range (ultra meaning too short a wavelength). In the same way that infrared wavelengths are too long for us to see. In optics, basically anything beyond blue is referred to as UV until you get to other stuff like X-ray. The reason is partly laziness and partly that there aren't many functional uses for violet light, whereas UV is used for all sorts of things.
There are several different classes of UV light, just like there's many shades of blue or classes of infrared (near, long-wave, mid-wave, etc).
The reason that you can see light from "UV" lamps is because they're usually emitting over a range of wavelengths and some of that falls in the visible spectrum. And on the other end, some infrared LEDs emit a little bit of red light which is visible.
If something isn't visible it matters for safety. Most of your eyes' defense mechanisms rely on limiting the amount of light entering your pupils, so they need to be able to perceive how bright a light is. Strong UV is particularly dangerous because it's high energy (think sunburn) and you can't see it so you won't reflexively blink and your pupils won't close. Infrared can also be dangerous, but it's a lower wavelength so you need more of it to do damage.
>Do spectral violet and ultraviolet differ? In what way?
It's ultra because it isn't within the visible spectrum. Violet is a spectral color, which means it's evoked by a single wavelength of light. So the term spectral violet refers to all the shades of violet.
Ultraviolet refers to wavelengths of light which are just a little bit outside the range which humans can perceive. It is not visible.
Some fluorescent materials can be lit with UV light, because they will fluoresce at wavelengths we can see. Otherwise, UV lamps also emit visible wavelengths.
This is a bit of a nitpick, but most people (especially children) can see at least a bit into UV. With my contacts in, I can see down to about 400-410nm. With them out, I can see to about 390nm, because the plastic in the contacts blocks shorter wavelengths. I tested this using a spectrophotometer.
People who have had cornea-replacement surgery and opted for the UV-transparent corneas can see further into the UV.[1] A child (with young corneas that haven't yellowed at all) almost certainly can too.
Slighly off topic, but UV visibility is important in other species. See this link for photos of flowers showing how they appear to bees or birds.
The CIE charts don’t really consider how to interpret or recolor data outside the color space, for example the UV reflection from flowers or astronomy photos in the UV/X-ray spectrum.
Yes, sunlight plus a good prism, inside a box with a pinhole, projecting on white paper. Or a room with a window that faces the sun, covered except for a pinhole, projecting on a whitewashed wall. Which is what Newton did, or so I've read.
Anyway, when I do that, my moderate red-green color blindness is obvious. Because there's a gap in the spectrum. But on a good computer display, there's far less of a gap, because colors aren't spectral, just mixed. For example: https://www.deviantart.com/0bsidianfire/art/Sanguine-4676007...
The point is that you need a source which contains the wavelength of interest. Monitor leds are red/green/blue and don't emit violet photons. 405nm is usually somewhat visible, if a bit blurry. Blue leds are usually Gallium Nitride based which produces more like 450nm.
Look up the photopic and spectroscopic response:
https://en.m.wikipedia.org/wiki/Luminosity_function
https://en.m.wikipedia.org/wiki/Photopic_vision
https://en.m.wikipedia.org/wiki/Scotopic_vision