Why can't light be in black color?

[Anithadhruvbud]

There are different colors of light that I have heard about but when I asked this question to my physics teacher she said I should ask the sun about it.So what do you guys think? Can't it be in black color maybe we are not able to see such a kind of light or maybe it exists it some other galaxy?

 

[Grinkle]

Sounds like your physics teacher is prompting you to do some thinking about concepts so you can pose your questions in a more addressable form.

Black in the context of your question is, imo, an interpretation by the human brain of an absence of detectable light or also obtainable as a mixture of some pigments and in that context black is just as much a color as any other color our brains perceive. You can certainly buy a pen that is filled with black ink, and anyone you ask would agree that indeed the ink in the pen is black.

These are not deep observations - that is why I think your physics teacher is wanting you to spend some more energy thinking about concepts.

 

[cnh1995]

I'm no expert in optics but I believe colour is what our eyes make of the light falling on them. Black is simply absence of visible light. In space, everything looks black except for the blinking stars. Our eyes decide which colour it should be, when light falls on them. If no radiation from visible spectrum falls on the eyes, they treat it as 'black'. But for colour blind people, everything is black and white only. So, for human eye, 'black' is absence of visible light.

 

[davenn]

In space, everything looks black except for the blinking stars.

just a note, when in space and observing the stars, they don't blink/twinkle ... it is when observing from Earth that they are seen to twinkle
due to atmospheric distortion as the starlight passes through it

 

[HallsofIvy]

Start with your definition of "black".The concept of whether black is a color is a matter of debate, and it depends on the context and how you define "color."

In terms of pigment and paint, black is often considered a color. When you mix different colors of pigment together, as in the subtractive color model, combining various colors eventually results in a darker color that can be described as black. For example, mixing cyan, magenta, and yellow pigments in equal proportions can produce a dark color resembling black.

However, in terms of light and the additive color model, black is not considered a color. In this model, colors are created by adding different wavelengths of light. When you combine all the colors of light at full intensity, you get white light, while the absence of light results in darkness, which can be described as black. In this sense, black is the absence of color.

So, whether black is a color or not depends on whether you're considering it in the context of pigments or in the context of light. It's important to note that the definition of "color" can vary in different contexts, and this leads to varying interpretations of whether black qualifies as a color.

 

[rootone]

There are actually things which go by the popular name of 'black lights'.
What they are in fact is UVA lights, florescent tubes usually, (UVA is the lowest frequency UV range, not dangerous).
They're often used in discos and other entertainment events.
While the lights themselves are barely noticeable, their UV light reflects intensely in the visible range from other objects which are illuminated.

 

[Michael2525]

The colors we see are basically the colors that are reflected off of an object. So even if there was such things as black light, we wouldn't be able to see it because nothing reflects black since the color black is basically an absence of light.

 

[CWatters]

If you were designing a new type of solar panel you would want it to absorb all of the light that lands on it because any light that is reflected is wasted. Scientists are developing coatings to do this based on nano technology. Such a coating would not only appear very black but it would also appear to have no texture or contours. Indeed it would be hard for your eyes to focus on it because there is so little reflected light for your eyes to process.

 

[fresh_42]

https://curiosity.com/memes/vantabl...u-cant-see-this-1-vantablack-nikola-slavkovic

 

[cnh1995]

just a note, when in space and observing the stars, they don't blink/twinkle ... it is when observing from Earth that they are seen to twinkle
due to atmospheric distortion as the starlight passes through it

Right! I should have said 'sky' instead of 'space'!

 

[davenn]

uh huh ... no probs
just wanted to make sure the OP wasn't unintentionally led astray

It's been good on PF ... has helped me to improve in making sure I say things as accurately as possible
Love the forum, it's been awesome for learn and expanding ones knowledgeDave

 

[sophiecentaur]

A very good 'black' can be obtained by using a hole with a box behind it, lined with black velvet. Any light entering the hole (form any direction) will hit the velvet at the back and be mostly absorbed. Any light reflected off the back will be further absorbed by the velvet on the other sides. Hence no (or extrememly little) light will emerge from the hole. The hole will look much blacker than the blackest / most matt paint you can apply to a surface. It's quite impressive to see.
The method is (or used to be, in analogue days) used for setting up the 'black level' on TV cameras, in brightly lit studios. Circuits and devices are more stable these days and don't need to be calibrated so often so it's something you probably don't need in a studio all the time.

 

[Svein]

A very good 'black' can be obtained by using a hole with a box behind it, lined with black velvet.

The box doesn't even have to be lined with something black. I remember my first course in optics at the university (more than 50 years ago, by Jove) where the theory was explained. We were then shown such a box, the hole was extremely black. When the lecturer opened the box, it was covered with mirrors on the inside!

 

[Merlin3189]

... their UV light reflects intensely in the visible range from other objects which are illuminated.

Just to join the pedants, can I point out that reflected UV light is still UV and just as inconspicuous. Look in a mirror. Look at many white surfaces.
Your intense "reflection" is actually caused by fluorescence not reflection. The UV is absorbed and visible light is emitted. The reason that white fabrics and some papers often do this, is because they are treated with "optical brighteners". These chemicals are intended to absorb the normally invisible UV in natural light and convert it into visible light, making the fabric appear "whiter than white".

But Hallsoflvy has it - first decide what you mean by black. Some people here are using the definition I prefer - the absence of light. By that defn black can't contain any other light.
There is also the psychological notion (I find it hard to call it a definition, without further qualification) of something which looks black. In that case of course black can contain any or all colours. For example looking at a blackboard you probably see much the same colours as when you look at the white chalk - just not quite so much of them (but a lot more than you might think.)

 

[fresh_42]

Some people here are using the definition I prefer - the absence of light. By that defn black can't contain any other light.

Couldn't it simply be defined as 0°K?

Edit: I've added the '°' although I didn't like it, just to distinguish it from 'o.k.'

 

[Buckleymanor]

There are different colors of light that I have heard about but when I asked this question to my physics teacher she said I should ask the sun about it.So what do you guys think? Can't it be in black color maybe we are not able to see such a kind of light or maybe it exists it some other galaxy?

Does light have a colour until it interacts with an object?
Can we see it as a laser beam or is it the small objects within the beams focus that interact with the radiation and glow as colour making it visable.

 

[jbriggs444]

Does light have a colour until it interacts with an object?
Can we see it as a laser beam or is it the small objects within the beams focus that interact with the radiation and glow as colour making it visable.

Light has a spectrum whether or not we can see it. Shine a ruby laser into space and we can say that the beam is red, even though it may never be seen. No need to make things complicated.

"If a tree falls in the forest, does it make a sound? Yes -- the bigger the tree the bigger the sound" -- Jim Ignatowski

 

[fresh_42]

Light has a spectrum whether or not we can see it.

Yes. But the term 'color' is already a measurement (by our eyes). So before we define 'black' or 'black light' we should not forget to define 'color'.
I've always asking myself whether we both 'see' the same color if we say 'it's red' and how can we know?

 

[HallsofIvy]

Does light have a colour until it interacts with an object?
Can we see it as a laser beam or is it the small objects within the beams focus that interact with the radiation and glow as colour making it visable.

It depends on exactly what you mean by "color". Light has (a range of) frequencies and wave lengths, that determine its color, before it interacts with an object.

 

[rootone]

...
Your intense "reflection" is actually caused by fluorescence not reflection.

I agree with that correction.

I've always asking myself whether we both 'see' the same color if we say 'it's red' and how can we know?

Wavelengths in the region of around 650nm are 'red'.
Two different people (without visual impairment) will agree that that is red.
Different instruments can determine the exact wavelength.
Comparing experiences of 'redness' isn't really within the domain of science, and I guess most philosophers would pass on that one too.

 

[fresh_42]

Comparing experiences of 'redness' isn't really within the domain of science, and I guess most philosophers would pass on that one too.

In biology it is. Color is an agreement, of course physically defined by a wavelength. To question its domain of validity in living species is IMO legitimate.

 

[HallsofIvy]

I know that each eye sees objects with two slightly different shades.

 

[Buckleymanor]

Light has a spectrum whether or not we can see it. Shine a ruby laser into space and we can say that the beam is red, even though it may never be seen. No need to make things complicated.

"If a tree falls in the forest, does it make a sound? Yes -- the bigger the tree the bigger the sound" -- Jim Ignatowski

I am not trying to complicate I just wish to know .
Whether light has a spectrum is dependent on the substance or object light is reflected or refracted by.
So to see a ruby red laser light, the light first has pass through a semi transparent substance in this case a ruby crystal.

 

[Buckleymanor]

It depends on exactly what you mean by "color". Light has (a range of) frequencies and wave lengths, that determine its color, before it interacts with an object.

Yes the substance the light passes through first, determines it's wavelength.Light from an incoherent source is invisible until it interacts with an object.I suppose you could argue that light from the sun has slight yellow hue due to it's interaction with it.

 

[CWatters]

I am not trying to complicate I just wish to know .
Whether light has a spectrum is dependent on the substance or object light is reflected or refracted by.

Light has a colour or spectrum of colours before and after it is reflected or refracted. It might not be the same colour or spectrum of colours before and after.

 

[Grinkle]

Does light have a colour until it interacts with an object?
Can we see it as a laser beam or is it the small objects within the beams focus that interact with the radiation and glow as colour making it visable.

Whether an object has color is a more interesting question, imo. If you see a red carpet, you are seeing the red wavelength photons the carpet reflects and you are not seeing all the other photons the carpet absorbs. So what you are seeing is, in some sense, what the object is NOT, you are seeing that which the object rejects. All of the photons the object absorbs, whose energy or substance or whatever goes into the object, you are NOT seeing.

Light has color - it is composed of photons with wavelengths, and when a photon hits your eye, your brain perceives the wavelength as color. imo there can be no doubt that light has color, red / green / purple etc are just a catch-all terms for certain subsets of photon wavelengths, and photons have wavelengths (or frequencies if one prefers). A photon will be emitted by something and hit your eye for you to perceive its wavelength, but it had the wavelength before it hit your eye, and would continue to have it even if it never did hit your eye. If a tree falls in the forest, it makes a noise, in that it causes ripples in the air, even of no ears are there to intercept those ripples.

 

[Buckleymanor]

Light has a colour or spectrum of colours before and after it is reflected or refracted. It might not be the same colour or spectrum of colours before and after.

From that it sounds like a spectrum of colours has colour .White light is made up of the spectrum but we don't see it as a full of colour it is only when it is broken into it's constituent parts by passing the white light through a prism do we see colour.White light is quite invisible otherwise the night sky between the stars would not be dark.

 

[jbriggs444]

From that it sounds like a spectrum of colours has colour .White light is made up of the spectrum but we don't see it as a full of colour it is only when it is broken into it's constituent parts by passing the white light through a prism do we see colour.White light is quite invisible otherwise the night sky between the stars would not be dark.

All light is invisible in the sense that it does not reflect light and it does not glow -- you cannot see a beam of light unless there is some dust to scatter it toward your eyes [or unless you stare directly into the flashlight]

The fact that the night sky is black has essentially nothing to do with the color of the light from the stars and everything to do with the fact that there is nothing out there to scatter that light.

 

[Merlin3189]

White light is made up of the spectrum but we don't see it as a full of colour it is only when it is broken into it's constituent parts by passing the white light through a prism do we see colour.

Most light that we see is made up of a spectrum of colours. The only light we see which IS a single colour (more or less) is from a laser, from a narrow band filter, or from a monochromator (where light is split up by a prism or diffraction grating.) Even after passing light through a gelatin filter or reflecting it off coloured objects, it is generally still a mixture of many colours - just with one predominating.

White light doesn't look coloured because the different colours it contains are balanced.
All white lights are not the same. Several lights that we say are white (say from different lamps, the window, burning magnesium, ...) if we compare them side by side, we then think some a bit pinkish, some a bit bluish, others maybe still white but different. This is known as the colour temperature of white light.
Yet again you could have two white lights that do look identical (to your eye), but when analysed with a spectrometer (put through a prism) show very different spectrums (different mixtures of colours.) White light from an incandescent bulb has a spectrum that contains ALL the colours of the visible spectrum and the spectral graph is a smooth distribution. Light from a flourescent lamp or LED lamp usually contains 4 bands of colours and its spectrum looks completely different. (Try looking at different lamps with your prism, or reflected in a CD if you don't have a prism.) Manufacturers vary the amounts of each colour to produce different whites, like warm white (more red) and cold white (more blue).

From that it sounds like a spectrum of colours has colour .

So it depends on the mix of colours in the spectrum. If there is the right balance of some red light, some blue and some green you see it as white. And a mixture of just two colours around red and cyan would look white. If the mixture is deficient in blue (mainly red and green lights) it looks yellow. If you reduce the green a bit as well, it becomes orange. The yellow light could contain lots of colours in the range red - orange - yellow - green, or it could simply be a mixture of two pure colours red and green.
Any colour you see can be made up of an infinite number of different mixtures. What you see depends on the balance of all the different components. (And incidentally on other factors such as context and the recent history of your eye. *)
You might like to have a look at a CIE chromaticity diagram. It tries to show how different mixtures of light will appear to a standard eye.

only when it is broken into it's constituent parts by passing the white light through a prism do we see colour

Or when anything upsets the balance of colours which makes it look white. So reflecting white light off a coloured object upsets the balance and let's you see the colour. Or passing white light through a filter.

White light is quite invisible otherwise the night sky between the stars would not be dark.

This is puzzling. You may be talking about Olber's paradox, but probably not. I think you are saying something like, "you can't see light unless it enters your eye." I don't think anyone would disagree with that!
But why would you say that? Are you thinking that if you look at a light beam which is not going into your eye, rather across your line of view or even away from you, then you can see it? That is because as the light goes through the air, a small part of it gets scattered so that it changes direction and does come into your eye. When people are taking photographs of lasers, they sometimes blow smoke into the beam to increase this effect and make the beam more visible.
If so, then that applies to white light and to coloured light. What is different is the degree of scattering for different colours. White light (a mixture) going through the sky has more of its blue light scattered than red. So the sky looks blue because we see this blue light scattered towards us from the white(ish) sunlight going in all directions which would not normally enter our eye. At sunset when we look at the white light from the sun, it looks red (and dimmer) because so much blue has been lost in scattering.

(*) If you have a coloured filter such as a piece of red, green or blue cellophane, try holding it over one eye only for a minute, then when you remove it, look alternately through each eye. Obviously while you wear the filter, things will look different colours through each eye. But when you remove it, things will still look different through the two eyes for a few seconds. This is because you have changed the balance of sensitivity to different colours in your eye. They return to normal soon when thet are both exposed to similar light again.

 

[Buckleymanor]

All light is invisible in the sense that it does not reflect light and it does not glow -- you cannot see a beam of light unless there is some dust to scatter it toward your eyes [or unless you stare directly into the flashlight]

The fact that the night sky is black has essentially nothing to do with the color of the light from the stars and everything to do with the fact that there is nothing out there to scatter that light.

I did not mention that the colour of the light from the stars had anything to do with the invisibility of light I actually said "otherwise the night sky between the stars would not be dark".
If you stare into a flashlight you are looking at the source of the light which is scattered by the filament and lense so of course you see it.
As for invisible light you don't need the the stars in the distance to imagine that its objects scattering the light that makes it visable.
There is one huge star the sun and the light from that is also invisible in the night sky.
Which brings me back to the main point that white light is invisible.

 

[jbriggs444]

Which brings me back to the main point that white light is invisible.

Again, you have said that "white light is invisible" when the word "white" is completely irrelevant. It is the presence of that irrelevancy that prompted both my previous response and this one.

Edit to add...

In the context of staring into a flashlight, I would have said that we see light that is "emitted" by the glowing filament and is "collimated" by the lens. The term "scattered" is not the best fit.

It appears that we do not disagree about the physics but only on the phrasing that is used to describe it.

 

[pbuk]

I think there is still a fundamental misunderstanding here. There is no sense in which red light is visible but "white" light is not. The light emitted by a ruby laser is not white light that has been coloured by the crystal, the light emitted by the laser is of a single wavelength which our eyes perceive as red.

 

[Buckleymanor]

Again, you have said that "white light is invisible" when the word "white" is completely irrelevant. It is the presence of that irrelevancy that prompted both my previous response and this one.

Edit to add...

In the context of staring into a flashlight, I would have said that we see light that is "emitted" by the glowing filament and is "collimated" by the lens. The term "scattered" is not the best fit.

It appears that we do not disagree about the physics but only on the phrasing that is used to describe it.

I agree .Though the red laser explanation threw me.Does the light from the ruby laser have to be scattered by objects within it's path or is it a specific of a wavelength that can be seen in empty space.

 

[pbuk]

I agree .Though the red laser explanation threw me.Does the light from the ruby laser have to be scattered by objects within it's path or is it a specific of a wavelength that can be seen in empty space.

Light travels in straight lines. If the laser is pointed towards your eye, you can see it (don't try this at home folks). If the laser is not pointed towards your eye, you can't see it (you might however see some particles of dust or vapour that are illuminated by the laser, particularly if it is a powerful one that you REALLY don't want to enter your eye directly).

The reason the space between stars in the night sky looks dark is not because light is invisible, it is because there is nothing in that direction from which light is traveling towards your eyes.

 

[alw34]

'Black light' is all the light outside the visible spectrum.

"The light that excites the human visual system is a very small portion of the electromagnetic spectrum."

"The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object has a different meaning, and is instead the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.

https://en.wikipedia.org/wiki/Electromagnetic_spectrum#Visible_radiation_.28light.29