What makes black light?

Question

I'm just asking to make sure because I heard that black light is all of the wave frequencies (like white light) just all in different amounts.. is this true?

Answer 1

Hmmm, the other answerers are describing black, which is the absence of light. But I'm guessing you are talking about black light, which is the stuff that makes things glow (especially my shoe laces). And that is something completely different than 'black'. Let's assume that's what you are talking about.



No, black light is not all the frequencies of light in different proportions. Actually, neither is white light. White light is the sum of all frequencies of VISIBLE light. But there is stuff both above and below visible light frequency. And that is not part of white light... well it could be, but it need not be. You see that stuff that is above or below the frequency range of visible light is not visible to humans. Below the visible range, there is infrared, microwave, and radio wave. None of that can be seen by the human eye. Above visible light is ultraviolet (UV), xray and gamma ray. None of that is visible to humans either. So whit light need only have stuff from red to violet in the spectrum. The sun has that and a bit of UV and a lot of infrared, but the UV and infrared are not noticed by your eye.



Now back to black light. Black light is UV light. It the stuff above visible in the frequency range. Sometimes black lights look a little bit violet, that is because they often have a little bit of the highest frequency visible light, which is violet. But a perfect black light would not have that violet. It's called black light because you can't see the light. It is out of the humans visual range. However, it makes stuff glow. And the reason for that is the UV light gets absorbed by certain materials. Once it is absorbed, it gets down-converted in energy and re-emitted as lower energy (and thus lower frequency) light. This lower frequency is usually visible light, so you can see the emitted light. Not everything glows under a black light. Things need to be fluorescent to glow under a black light. Some things are more fluorescent than others, and it depends on the chemical makeup of the material being illuminated. Things like fluorescent markers are very fluorescent. So are scorpions for some reason (no kidding, that is how they find them - using a black light!). Most laundry detergents companies will add a fluorescent pigment to the laundry detergent. This makes the clothes look even whiter under sunlight, because the pigment absorbs the UV sunlight and turns it into visible light, making the clothes a smidge brighter.



Black light has to be UV (it can't be infrared) because the 'black' photons need to have more energy than the visible light, so that when they lose energy during the re-emission, they can be visible. If they were infrared, they would lose energy and become something even farther from visible. Light can't (for almost all intents and purposes) gain energy in this process. So the light needs to be UV. It could xray too, but that is too much energy and other issues make that not work. Because this is UV light, black light is not a good thing to look at. The re-emitted light is fine to look at. But it isn't a great idea to look directly into the bulb. It's not going to blind you right away or anything, But still, it's best to avoid looking at the bulb.

Answer 2

no, this is not true. here's why:



when pure (white) light hits an object, the object absorbs some of that light, and reflects the rest. the light that is reflected is the light that we see.

for example, imagine white light hitting a plant, then hitting your eye. we see that the plant appears green. here's what's actually happening: the white light hits the plant and every other color except green is absorbed by the plant. the green light (light of a specific energy or wavelength) is reflected back, and that is what we see.



"black light", on the other hand, is the absence of reflected light. if you were to observe that an object appears black, what is actually happening is the object has absorbed every wavelength of the white light that hit it, and reflected none of it back.



we can see this because we notice that black objects are often hotter than white ones. for example, if you touch a black car that has been sitting in the sun all day, it would be much hotter than a similar white car. in another example, you may have noticed that if you wear black on a hot day, you feel much hotter than if you were to wear white.

this is because the black object (car/clothes/etc...) has absorbed much more energy from the light (because it took in the light energy), whereas the white car reflected it all away.



hope this helped! any questions on what i said?

Answer 3

Hey Anna,

Black light is NOTHING, literally. Its no way a combination of all the wavelengths. On the contrary, its a state of absence of any visible wavelength.



Hope its clear enough.