What Gives Light its Glow and How Does its Speed Change on Earth?

In summary, light does not illuminate something by traveling by it or in it. Instead, light has to reflect off something and enter the eye in order to be sensed by the retina, making the object appear brighter. The speed of light in air is slightly slower than in a vacuum due to the process of absorption and reemission as it passes through atoms. Photon interactions are responsible for keeping electrons and protons apart in atoms, preventing them from collapsing on each other. In a dark room, there are still photons present, but they are not visible without something to reflect off of. The color of light is a combination of different wavelengths in the electromagnetic spectrum, with visible light ranging from 450nm to 700nm. When matter heats up
  • #1
neoweb
24
0
What makes light "glow"?

Hi,

First post from a newbie... so forgive the naivety...

Light is described as an electromagnetic wave/particle... but what actually gives light its "brightness", allowing it to illuminate the surroundings through which it travels?

Also, another question if i may... I know that the speed of light, 186,000 miles per second, refers to light speed in a vacuum, however is the speed of light on Earth (through air that is) much different? How much slower is it?

Thanks in advance for all your help.
 
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  • #2
light does not illuminate something by traveling by it or in it. Light has to reflect off something, and eneter your eye in order to be senced by your retna, making the object seem brighter by the light.

To answer your second question. The speed of light in air is a little less, not much. But the reason there is a difference is because as light propagates throught a medium such as air, it has to go throught atoms (oxygen atoms, nitrogen etc..) What happens is a photon of light will hit an electron in the atom, cause it to shift to a higher energy level, and then go back down to the original and emit the photon again so it goes to the next atom. It is like a chain reaction. The proces of absorbtion and reemitttion is what makes light seem slower while traveling in air, because of this little delay in propagation.
 
  • #3
Nenad said:
light does not illuminate something by traveling by it or in it. Light has to reflect off something, and eneter your eye in order to be senced by your retna, making the object seem brighter by the light.

Oh yes, silly me... so the retina/brain "converts" the electromagnetic wave to give vision...

I read recently that photons are largely responsible for why matter doesn't collapse in on itself!? For example, the electrons (negatively charged) and protons (positively charged) inside each of the atoms that make up our bodies should ordinarily attract each other and thereby cause us to collapse in a heap(?), however, because photons interact between electrons and protons this interaction suffices to keep the two apart. Does that sound about right? (p.s. I may also post this in the quantum physics forum)

Related to the last point above... are there still photons in the air when it is pitch black?
 
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  • #4
neoweb said:
Oh yes, silly me... so the retina/brain "converts" the electromagnetic wave to give vision...

I read recently that photons are largely responsible for why matter doesn't collapse in on itself!? For example, the electrons (negatively charged) and protons (positively charged) inside each of the atoms that make up our bodies should ordinarily attract each other and thereby cause us to collapse in a heap(?), however, because photons interact between electrons and protons this interaction suffices to keep the two apart. Does that sound about right? (p.s. I may also post this in the quantum physics forum)

to answer you atomic question. Yes this is right, according to quantom theory, there are things called virtual photons which are responsible for the elctromagnetic force. These virtual photons ar what keeps elevtrons and protons appart in an atom.


neoweb said:
Related to the last point above... are there still photons in the air when it is pitch black?
yes, try it. Turn off the light in a dark room and shine a flashlight past the door, you will see that you see nothing in the room. You might see dust particles, but this is because they bounce the photons to your eyes, but you do not see the back of the room.
 
  • #5
Hmm, then, why is the colour of light white? Is it because of its speed? Because, if a matter goes fast, it heats, so it turns into an incandescent matter, and as i know when a matter turns into an incandescent matter, its colour turns into white. Is it becaouse of that, or...?
 
  • #6
canopus said:
Hmm, then, why is the colour of light white? Is it because of its speed? Because, if a matter goes fast, it heats, so it turns into an incandescent matter, and as i know when a matter turns into an incandescent matter, its colour turns into white. Is it becaouse of that, or...?

its not actually white, its a combination of 5 main coulours in the elctromagnetic spectrum. The waveleangth of visible light varies from 450nm to 700nm, and this variation produces different colours (violet, blue, green, yellow, red). And about your second claim, when matter heats up, it releases different colours of light. This is called blackbody radiation. It can be summed up using Weins law.
[tex] {\lambda}T = 2.9 * 10^{-3} m*K [/tex]
 
  • #7
canopus said:
Hmm, then, why is the colour of light white? Is it because of its speed? Because, if a matter goes fast, it heats, so it turns into an incandescent matter, and as i know when a matter turns into an incandescent matter, its colour turns into white. Is it becaouse of that, or...?

Light is one of the hottest things there is, since heat is really kinetic energy. But light can't go faster or slower, so I doubt that makes it red-green-blue...

Speaking liberally, light has no "color", it only has a frequency. Our eyes interpret this and we assigned the different frequencies the name of "color".
 
  • #8
Hmm, now i could understand clearly! Thanks...
 
  • #9
In regards to light traveling through a medium:
When a photon collides with an electron, the electron momentarily goes up an energy level and then back down at which point another photon is emitted. I’m curious as to why the photon that gets emitted continues on in the same direction as the initial colliding photon. Can anyone elaborate?
 
  • #10
check said:
In regards to light traveling through a medium:
When a photon collides with an electron, the electron momentarily goes up an energy level and then back down at which point another photon is emitted. I’m curious as to why the photon that gets emitted continues on in the same direction as the initial colliding photon. Can anyone elaborate?

Conservation of momentum.

Yep, that about sums up my knowledge on that one.
 
  • #11
Hmm..
I'm aware that the atom produces a photon of the same frequency as the one that hit it in the same direction, but what happens to the initial photon? If I remember correctly, lasers use this property to function properly. If the photon that strikes the atom doesn't continue, then how would lasers function?
 
  • #12
Alkatran said:
Conservation of momentum.

Yep, that about sums up my knowledge on that one.

Photons have weight?
 
  • #13
JasonRox said:
Photons have weight?

Photons have no rest mass, but they have momentum. I believe it is calculated with their frequency, the higher the frequency the higher the momentum.
 
  • #14
How could you say that light glows, had you ever saw a path of light. It make things possible to see when it transfer information about the thing to our eyes and our brain visulize it. it something like the thing you want to see has coded some information and send it as EM wave and our eyes and brain decoded in the same manner in which it was encoded. Take an example of a computer as you save any ingormation in it like a written text then it doesn't save itself as the text it appears.
 
  • #15
Nenad said:
its not actually white, its a combination of 5 main coulours in the elctromagnetic spectrum. The waveleangth of visible light varies from 450nm to 700nm, and this variation produces different colours (violet, blue, green, yellow, red).
[tex] {\lambda}T = 2.9 * 10^{-3} m*K [/tex]

Uhhh... Another thing... In software programs on the computer like photoshop... there's options of magenta, yellow and cyan, and red, blue and green. When you mix equal amounts of 100% red, blue, and yellow you get white. When you do the same with magenta, cyan, and yellow, you get black. On the TV there's red, green, and blue. Why the differences? Couldn't you create violet, and green out of the red, blue and yellow combo?
 
  • #16
aekanshchumber said:
How could you say that light glows, had you ever saw a path of light. It make things possible to see when it transfer information about the thing to our eyes and our brain visulize it.

Thank you... but this specific point has been asked and answered already above. See my second post.
 
  • #17
Mk said:
Uhhh... Another thing... In software programs on the computer like photoshop... there's options of magenta, yellow and cyan, and red, blue and green. When you mix equal amounts of 100% red, blue, and yellow you get white. When you do the same with magenta, cyan, and yellow, you get black. On the TV there's red, green, and blue. Why the differences? Couldn't you create violet, and green out of the red, blue and yellow combo?

Im not an artist, so I can't answer you question. But quantum mechanics is not art. The reson there is violet and blue at the bottom of the spectrum is because of its high frequency and very low waveleagth. You can't mix monochromatic light in order to get a high frequency colour.
 
  • #18
So Nenad, you're looking at a color monitor. Look closely: all colors are composed of red green and blue. So how does your monitor display violet? The reason you can get any perceived color out of just 3 color guns is because your eye itself has 3 different sensors each with its own spectral sensitivity. These all overlap heavily. Thus completely different colors actually can look exactly the same. E.g. a pure violet looks exactly the same as a combination of RGB. Here is a really excellent explanation (needs powerpoint viewer): http://people.cs.uct.ac.za/~jgain/courses/advgfx/colour.ppt
 
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  • #19
Mk said:
Uhhh... Another thing... In software programs on the computer like photoshop... there's options of magenta, yellow and cyan, and red, blue and green. When you mix equal amounts of 100% red, blue, and yellow you get white. When you do the same with magenta, cyan, and yellow, you get black. On the TV there's red, green, and blue. Why the differences? Couldn't you create violet, and green out of the red, blue and yellow combo?

If the RGB combination = violet, than are there also cyan, magenta, and yellow combinations for violet?, about RGB, on a cathode-ray tube based monitor, how does yellow appear?
:confused:
 
  • #20
meh, if you think about it, that is only a way for us to see it. If we were actually to think about the quantum particles, it would be impossoble.
 

1. What is light and how does it glow?

Light is a form of electromagnetic radiation that is visible to the human eye. It is produced when electrons in an atom move from a higher energy level to a lower energy level, releasing energy in the form of photons. This process is known as luminescence, which is what causes light to glow.

2. What makes certain objects glow in the dark?

Certain objects are able to glow in the dark because they contain materials known as phosphors. These materials have the ability to absorb energy from a light source, such as the sun or a light bulb, and then release that energy in the form of light over a period of time. This process is known as phosphorescence and is what allows objects to glow in the dark.

3. Why do different colors of light glow differently?

The color of light is determined by its wavelength, with shorter wavelengths producing blue and purple light, and longer wavelengths producing red and orange light. When an object glows, it emits light at a specific wavelength depending on the energy level of the electrons involved. This is why different colors of light glow differently.

4. Can artificial light sources also produce a glow?

Yes, artificial light sources such as fluorescent bulbs and LED lights can also produce a glow. These light sources use electricity to excite gas molecules, causing them to emit light. This process is known as fluorescence and is commonly seen in products such as glow sticks and blacklights.

5. How does the intensity of light affect its glow?

The intensity of light refers to the amount of energy or brightness of the light. The higher the intensity, the brighter the light will appear. This is because higher intensity light contains more photons, which can cause more electrons to move and emit light. Therefore, the higher the intensity of light, the more intense the glow will be.

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