I already know that visible light is only a tiny fraction of the electromagnetic spectrum, and just after that comes UV radiation, since its wavelength is shorter and thus frequency is higher. My question is: if you can ONLY see visible light, then why can you often see UV light as purple? Isn’t it supposed to be invisible? I’m referring to those commercial torches that emit UV (and purple) light.
In: Physics
its in their name ” Ultra Violet” while the light you actually care about is not actually visible some of it will and this visible part of it will be at the edge of the violet spectrum of visible light . we cant avoid this because its very difficult ot have a bulb that only emits one type of radiation.
Any UV source will likely emit some shortwave visible light as well, which looks purple/violet. As mentioned by others, that’s a good thing so we know it’s on.
In addition to what other people have said, we all expect it to be purple so why filter that out and add a green or red light now? Like you know when there’s ultra violet light this way. Sort of like how we could make car doors much quieter, but choose not to for ease of use.
The electromagnetic spectrum is vast and humans only see a small portion of it, which we call visible light.
The visible light range is:
Infrared <—| Red – Orange – Yellow – Green – Cyan – Blue – Violet |—> Ultra Violet
As you can see violet is right next to the Ultra Violet range. Humans can’t see Ultra Violet, but the lamps we buy are imperfect (perhaps by design) and some of the light is released in the visible violet light range.
First, to answer you question as best I can:
The UV light component is invisible, but the light source also emits visible violet light. I don’t know whether that’s a physical limitation or a safety issue (if you can’t see the light, you can’t tell if it’s on).
Second, it’s violet, not purple. Violet is its own color, with a specific wavelength range. Purple is a mix of two or more colors (reds and blues), each with their own wavelength. To our eyes, it’s a subtle difference, but they’re thus very different on the physical level.
We don’t see UV as purple. If UV lamps only emitted UV light, it would look as like it was off. We don’t do that for a few distinct reasons.
1. It’s hard to make anything emit only UV, like anything, the lamps emit a spectrum of light, and it sort of bleeds into visible.
2. We could block out the purple that is made, but why should we, it gives a very easy way to tell if your UV lamp is on or not, without doing much harm.
Ultraviolet is called ultraviolet because it is near violet in wavelength.
We can’t see ultraviolet itself, but light rich in UV is going to be rich in violet/purple light that we *can* see.
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