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What Does ''white'' Mean In White Light?

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#1 xyz

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Posted 18 October 2015 - 03:42 PM

What does white mean in white light?  what exactly is white light?



#2 pgrmdave

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Posted 19 October 2015 - 11:31 AM

From wikipedia: "White light is a combination of lights of different wavelengths in the visible spectrum. Passing white light through a prism splits it up into the several colors of light observed in the visible spectrum between 400 nm and 780 nm."

#3 xyz

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Posted 19 October 2015 - 12:22 PM

From wikipedia: "White light is a combination of lights of different wavelengths in the visible spectrum. Passing white light through a prism splits it up into the several colors of light observed in the visible spectrum between 400 nm and 780 nm."

So white light is something you send through a prism?

 

combination - ''a joining or merging of different parts or qualities in which the component elements are individually distinct'' 

 

What do you mean by visible spectrum ?  frequencies that are individually distinct from the constant?


Edited by xyz, 19 October 2015 - 12:27 PM.


#4 pgrmdave

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Posted 19 October 2015 - 12:42 PM

So white light is something you send through a prism?
 
combination - ''a joining or merging of different parts or qualities in which the component elements are individually distinct''

What do you mean by visible spectrum ?  frequencies that are individually distinct from the constant?


No, white light is a combination of many different wavelengths, comparable to how "white noise" is composed of many different sound frequencies. The visible spectrum is the range of electromagnetism that we're able to see (as distinct from things like radio waves, infra-red, x-rays, etc.)

#5 xyz

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Posted 19 October 2015 - 12:53 PM

No, white light is a combination of many different wavelengths, comparable to how "white noise" is composed of many different sound frequencies. The visible spectrum is the range of electromagnetism that we're able to see (as distinct from things like radio waves, infra-red, x-rays, etc.)

I am sorry I must be  slow on the up take or something, what exactly is this white light?  where can I observe it?  



#6 CraigD

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Posted 20 October 2015 - 07:13 AM

I am sorry I must be slow on the up take or something, what exactly is this white light? where can I observe it?

What’s likely confusing you, xyz, is the idea that “white” is a physically real color, that can be carried to your eyes by a single kind of physical thing.

In the case of light, the things that caries it are photons. Every photon has a single characteristic, its frequency (which can also be given as a wavelength) that determines the color that the eye would perceive a sufficiently numerous stream of them as. We perceive a stream of photons with frequencies around 440 THz (440000000000000 Hz) as red, around 550 as green, around 640 as blue.

We perceive a stream of a roughly equal mix of photons with around these three frequencies as white. We also perceive other mixtures of photons of different frequencies as white - a roughly even mix of photons with frequencies between 400 and 800 THz (we can’t visually perceive photons with frequencies much lower of higher than this) looks white. So the image of two objects that both look identically white to us may actually be carried to us with stream of photons with very different frequencies.

The reason for this is the way our eyes work. They have receptors - retinal cone cells - in them that respond most strongly to photons near the 3 red/green/blue frequencies, “averaging” them to give us our color perception. It’s fair to call the color white an optical illusion due to

I find it interesting to imagine what we and our civilization would be like if we had very different light perception organs, ones that could accurately perceive the frequency of each individual photon in a stream of light, like a scientific instrument. We would have intuitively known the true physical nature of light, which in real history took ‘til Isaac Newton’s discovery of it around 1666 AD. But it would have been much more difficult for us to make realistic representations of objects, such as color paintings, because our “eyes” would be more difficult to fool. A color video monitor, which requires just 3 kinds of light-emitting elements capable of emitting photons around the three RGB frequencies, would have to be capable of emitting photons of practically any frequency in our visual range. What our civilization would be like is hard to imagine with much conviction.

#7 xyz

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Posted 20 October 2015 - 12:11 PM

What’s likely confusing you, xyz, is the idea that “white” is a physically real color, that can be carried to your eyes by a single kind of physical thing.

 

Yes white is real physical colour, I have a piece of paper in front of me that is white, so how does this piece of paper differ from the yellow looking element of my light bulb and the light that gives out?



#8 pgrmdave

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Posted 20 October 2015 - 01:23 PM

Yes white is real physical colour, I have a piece of paper in front of me that is white, so how does this piece of paper differ from the yellow looking element of my light bulb and the light that gives out?


Different combinations of frequencies of light. The light reflecting off the white paper is less skewed toward one or another frequency than the light emanating from the light bulb, which is skewed toward frequencies we interpret as "yellow".

#9 CraigD

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Posted 20 October 2015 - 03:24 PM

Yes white is real physical colour,

This is true in the sense that you can call an object, like a piece of paper or a painted car or wall, “white”, but you cannot identify a frequency of light that corresponds to “white”.

A simple experiment that you can perform to demonstrate this is to take a beam of white light, such as sunlight, pass it through a triangular glass prism so that it shines onto a sheet of paper. White light will appear on the paper split into many different colored bands. Done with a source of white light such as cell phone screen displaying a white page, the light will appear split into 3 fairly sharp red, green, and blue bands. The light from a red laser pointer, however, will remain a single band of red light.
 

I have a piece of paper in front of me that is white ...

The paper is actually a pretty good reflector of visible light of all frequencies, so the color you perceive is due to how you illuminate it. Sunlight and most artificial light sources meant for general lighting provide a fairly even mixture of light of different frequencies (a spectum), so make the paper appear white. Light from a source covered with a simple filter that removes light of frequencies other than those for a specific color makes the paper appear that color.

So the paper in front of you is white because its illuminated with light with a fairly even spectrum. Were it otherwise, the paper would be colored.

A sheet of “colored paper”, or paper with colored ink, paint, etc. on it illuminated with sunlight or a general lighting artificial light works because the pigment on it absorbs light of frequencies other than those we perceive the paper as being.
 

... so how does this piece of paper differ from the yellow looking element of my light bulb and the light that gives out?

The paper reflects a slightly different spectrum than the light bulb emits, because it absorbs light of some frequencies more than those of others.

The color we perceive light source like flames and light bulbs to be is complicated, because it depends on what part of the light source we look at. Consider this picture of a flame from Wikipedia:
170px-Candleburning.jpg
which has parts that looks blue, white, and orange.
Consider this picture of a famous low-power light bulb from Wikipedia:
170px-Livermore_Centennial_Light_Bulb.jp
If you look carefully, you’ll notice that the center of the filament appears white, the edges of it yellow.

If you observe carefully, such as through holes cut in dark paper, you’ll notice that paper illuminated by an incandescent light bulb is more yellow that the same paper illuminated by a florescent bulb.

Part of why we perceive the paper to be white is because we know that paper is usually white. With special lighting, pigmented paper can be made to appear white, or white paper appear colored. Many tricks can be played using paper, pigments, light, and people’s expectations.

#10 xyz

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Posted 20 October 2015 - 03:57 PM

A simple experiment that you can perform to demonstrate this is to take a beam of white light, such as sunlight,

Thank you for the very informative post and information which I appreciate.    I think I am understanding but I am a bit confused about the above quote,    Sunlight does not look white like the sheet of paper it looks colourless, why is this?


Edited by xyz, 20 October 2015 - 04:00 PM.


#11 jab2

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Posted 26 October 2015 - 02:01 AM

Thank you for the very informative post and information which I appreciate.    I think I am understanding but I am a bit confused about the above quote,    Sunlight does not look white like the sheet of paper it looks colourless, why is this?

Something that is often neglected in discussing vision is that what the optical sensors in the eye experience are not equal to what the brain makes us think we see.  Our brain not only take input from the eyes to form a "picture" but other stimuli and even historic information too, thus giving us a picture vastly richer in detail that what was passed down the optical nerves.

 

For a species who has grown up with paper we will nearly always see paper as white, even if the light iluminating it is not what we call "white light", because we "know" from experience paper is white.  So even if the paper is not illuminated with white light our brain "adjust" the information to still tell us it is white.  This is why camera manufacturers must build a white balance feature into their cameras as the camera sensor show what it "sees" without adjustment, thus white paper that is not white.  Take a photo of the same piece of paper under sunlight, fluorecent light, and tungsten light without the colour balance adjusted, and see how the colour of the "white" paper differ.

 

So to get to your question of "white" and "colourless", I think we call light which is a mix of all frequncies "white", simply because we have decided to call a surface which reflect all frequencies in the same ratio as the incoming light "white".

Vision is actually a facinating field.  We "see" so much more than what the eye see.



#12 xyz

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Posted 26 October 2015 - 06:12 AM

Something that is often neglected in discussing vision is that what the optical sensors in the eye experience are not equal to what the brain makes us think we see.  Our brain not only take input from the eyes to form a "picture" but other stimuli and even historic information too, thus giving us a picture vastly richer in detail that what was passed down the optical nerves.

 

For a species who has grown up with paper we will nearly always see paper as white, even if the light iluminating it is not what we call "white light", because we "know" from experience paper is white.  So even if the paper is not illuminated with white light our brain "adjust" the information to still tell us it is white.  This is why camera manufacturers must build a white balance feature into their cameras as the camera sensor show what it "sees" without adjustment, thus white paper that is not white.  Take a photo of the same piece of paper under sunlight, fluorecent light, and tungsten light without the colour balance adjusted, and see how the colour of the "white" paper differ.

 

So to get to your question of "white" and "colourless", I think we call light which is a mix of all frequncies "white", simply because we have decided to call a surface which reflect all frequencies in the same ratio as the incoming light "white".

Vision is actually a facinating field.  We "see" so much more than what the eye see.

Thank you , yes white light is a mixture of frequencies a range of frequencies that we visual observe, a range our brain interprets as colour, any other frequencies out of this range such as radio waves we not observe.   A radio wave we can not see in space, it is invisible, the same as the light in space, it is also invisible and not white, would you agree with this?

 

The easy interpretation of this, is to imagine that all light propagating through space or the air is Ultraviolet, a range we can not see . 


Edited by xyz, 26 October 2015 - 07:39 AM.


#13 jab2

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Posted 26 October 2015 - 08:16 AM

Thank you , yes white light is a mixture of frequencies a range of frequencies that we visual observe, a range our brain interprets as colour, any other frequencies out of this range such as radio waves we not observe.   A radio wave we can not see in space, it is invisible, the same as the light in space, it is also invisible and not white, would you agree with this?

 

The easy interpretation of this, is to imagine that all light propagating through space or the air is Ultraviolet, a range we can not see . 

Yes, the "light" travel as photons through space, only when it interact with the eye and the optical signals are processed by the brain do we experience the sensation we call "colour".



#14 xyz

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Posted 26 October 2015 - 08:35 AM

Yes, the "light" travel as photons through space, only when it interact with the eye and the optical signals are processed by the brain do we experience the sensation we call "colour".

Yes indeed, but is the interpretation of colour, recognising the differentials of 400-800nm of matter or a medium interaction providing a temporal distortion of the constant which is invisible to sight and equal to sight?

 

hence , we see rainbows that are a differential frequency to the constant of ''ultraviolet'' space?

 

Things we observe of 400-800nm are different to the ''transparent'' to sight space?

 

different because of velocity change in the constant?

 

added - From what I have learnt from science and forum life , I get this - 

 

Reactants of matter or a medium is the opposition of the element to a change of form or molecular breakdown by an opposing force such as the transmission medium constant (EMR), that temporally opposes change due to the element's inductance, capacitance, and emittance that denotes total equilibrium entropy of the mass. A suggested built-up electrical field or a suggested magnetic field or magnetic resonance that resists the force of the constant transmission rate , decreasing the propagation speed of the constant flow through or onto the matter or medium, inverting through itself the propagation of light by reflection and permeable properties of the matter, creating a constant interference pattern of matter relative to permeable and reflective properties of the matter between 400nm-700nm, that can be visually observed by sight through the constant clarity of light propagating through space.
The clarity of light propagating through space, the quality of being clear in particular, a suggested second constant to all observers when there is sufficient intensity of EMR present. A suggested frequency of zero whilst EMR is propagating through space, an equilibrium to sight, that all observers can clearly observe  the reactant of matter through, that creates a frequency between 400nm-700nm known as spectral content, by the process of  EMR interaction with a concrete existence such as objects or a medium. 
I postulate that light is a state and we see by EM radiation being a communications protocol medium of inverted neutralised carrier signals of that which  is formed by matters resistance force to the opposing force of light thus giving propagation of EMR  pressure magnitude to spectral content, each of which content is capable of transmitting messages modulated, inverted into itself in it's perceived spectral content, that travels through the constant equilibrium of light to sight, a carrier signal to the brain, a communications protocol that is a system of digital rules for data exchange between light interactions with matter and within itself to the brain. 
The information exchanged through the neutral communication medium  constant, the main means of mass communication—that is governed by rules and conventions that can be set out in technical specifications called communication protocol standards.
 The nature of a communication, the actual data exchanged and any state-dependent behaviours, is defined by its specification and the brains ability to interpret this information.
The basic difference between a parallel and a serial communication channel is the number of electrical conductors used at the physical layer to convey bits, this effect can be attributed to the transfer of energy from the light to an electron in the matter. From this perspective, an alteration in either the amplitude or wavelength of light would induce changes in the rate of emission of electrons from the matter.
A parallel communication is a method of conveying multiple binary digits (bits) simultaneously. It contrasts with serial communication, which conveys only a single bit at a time; this distinction is one way of characterizing a communications link to the brain that also becomes a duplicate transfer by mirrored properties, a period of changing from one state or condition to another by receivership.
A communication channel or channel, that refers to a physical transmission medium such as the constant of light in passive dark space, or to a logical connection over a multiplexed medium such as light. A Synchronization of the coordination of events to operate a system in unison to sight. The familiar conductor of an orchestra that serves to keep the orchestra in ''time''.


Edited by xyz, 30 October 2015 - 03:19 AM.


#15 industry7

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Posted 27 February 2017 - 10:24 AM

xyz, I'm not sure where you are going with your last post, but let's just step back for a second.

 

"the same as the light in space, it is also invisible and not white, would you agree with this?"

 

I do not agree.  Visible light in space is still visible.

 

"Sunlight does not look white like the sheet of paper it looks colourless"

 

Why would you say that?  When you look at a sheet of paper, you see white.  When you look at the sun, you see yellow.  Why would you say sunlight is colorless?



#16 exchemist

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Posted 27 February 2017 - 11:27 AM

xyz, I'm not sure where you are going with your last post, but let's just step back for a second.

 

"the same as the light in space, it is also invisible and not white, would you agree with this?"

 

I do not agree.  Visible light in space is still visible.

 

"Sunlight does not look white like the sheet of paper it looks colourless"

 

Why would you say that?  When you look at a sheet of paper, you see white.  When you look at the sun, you see yellow.  Why would you say sunlight is colorless?

This discussion died over a year ago. And xyz is quite bonkers. :)





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