Light

wurf · Sep 8, 2007

Does light from our sun differ in composition from light from other sources (i.e., fire from wood or wax, electric or flourescent bulbs)? Or is light just light?

MeteorWayne · Sep 8, 2007

All light is electromagnetic radiation in the band that our recievers (eyes) can detect. Every object has it's own unique spectrum of intensity vs wavelength (or it's inverse, frequency). So yes, sunlight differs from all other light sources. By the same token, all other light sources differ from all other light sources. Sort of like fingerprints or snowflakes. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

wurf · Sep 8, 2007

As I understand it, aside from its wave action, light also has a material property, the photon. Would a photon produced by our sun and one emitted from a light bulb be the same thing?

MeteorWayne · Sep 8, 2007

Yes, the only difference is the amount of energy (which in visual-land defines color, and in radio land wavelength and frequency.) <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

lukman · Sep 9, 2007

Photon has many different types? <div class="Discussion_UserSignature"> </div>

Saiph · Sep 9, 2007

the light itself is the same regardless of the source. One red photon is the same as any other red photon. However, sunlight as a whole is made up of a broad range of wavelengths of light, and the specific composition of this light is essentially unique to the sun (other similar stars have similar compositions, but not identical ones...like fingerprints). A fire, for instance, creates light by exciting air atoms and molecules. So it's going to show traces of light from Oxygen, Nitrogen and other atoms in the air. A Neon Light shows a range of wavelengths unique to the neon gas used in it's bulb. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

MeteorWayne · Sep 9, 2007

One type, many different amounts of energy in each packet. Radio waves are but different energy photons, so are X rays, microwaves, etc. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

heyscottie · Sep 10, 2007

Just like sound waves are all pressure vibrations in matter, and yet can have differing tones, light waves are all the same but can differ by frequency. All light sources will put out a spectrum, which can be shown on a graph with frequency on the x-axis and intensity on the y-axis. A red laser would have a spectrum that looks like a spike around its one frequency. Incandescent bulbs put out a wide spectrum, while fluorescent bulbs put out a spectrum with several spikes. (This is why CFLs do not reproduce color as well as incandescent bulbs.) Stars have differing spectra, too, which is how we can determine the type of fusion ongoing, as well as their speed relative to us. But they are all photons! Scott

lukman · Sep 10, 2007

Ok, i thought from the original question, as if there are many types of photon <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> </div>

emperor_of_localgroup · Sep 11, 2007

Sometimes a simple question make you think deeper. This is one of those questions. Sun light is also known as whitelight, because it appears to us as white but when passed through a prism the lights splits into its component clorors. If you look at spectrum of sunlight it appears as almost a continuous spectrum meaning all wavelengths of light is present in sun light. Saiph explained it well, but my question is why does it turn white? If a photon of a particular wavelenth comes out of an atom when an electron makes a transition, do this multiple photons from the sun interfere with each other and form a single wavelength which appears as white to us? Or is it the incapability of our visual system to separate the multy color light from the sun? I'll leave the artificial lights for others to explain. <div class="Discussion_UserSignature"> Earth is Boring </div>

adrenalynn · Sep 11, 2007

Color is a conceptual/psychological experience. Sunlight appears white because the colors you see split apart in the prism are additive. The eye/brain combines the wavelengths. It's a composite of all visible wavelengths of light. The frequency of emitted light depends upon electron transitions between the atomic energy levels of the source of the light. [edit: Sorry Ranur - I was having connectivity problems and didn't see you'd already responded. I was just trying to get my darned post to go through...] <div class="Discussion_UserSignature"> .bipartisan (bī-pär'tĭ-zən, -sən) [Adj.] Maintaining the ability to blame republications when your stimulus plan proves to be a devastating failure.IMPEACH OBAMA! </div>

MeteorWayne · Sep 11, 2007

Adrenalynn has it quite right. The 3 types of color detection cones in our eyes collect all the different photons and come up with an average. It is also significant that what we perceive as white is based on the color output from our star, hence our environment. Creatures on a planet around a red dwarf would probably see their sunlight as "white" The photons would be the same as we would see and measure them (i.e the energy of the photon, and the wavelength would be the same), but since it would be normal for their environment, their perception mechanism would see it as their "white". <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

adrenalynn · Sep 11, 2007

Yup! Then we have to get into emissive vs reflected light to talk about how we perceive color. The classic case is the red apple. Its physical makeup reflects far more strongly the frequencies of light that we perceive as "red" under white light A somewhat amusing exercise is to split white light into the components using a prism, and then pass the apple through each of those components. You'll see that the apple appears to change color slightly as it passes through each hue. We perceive color based upon the frequency of the light. The lowest visible being red (~ 625â€“740 nm), the highest is violet (~380-440 nm), and an although there are a nearly infinite number of hues in between, most people perceive something between 100,000 [ Mapping color perception to a physiological substrate Calkins, 1993, Visual Neurosciences] and 7 million [Myers, 1995, Psychology] distinct shades. The appearance of color is frequently measured using the HSB model. Hue, Saturation, and Brightness. The eye generally distinguishes about 150 hues. Brightness is the amount of light emitted or reflected, and Saturation is how "pure" or "intense" a color is. A really unsaturated color is very dull in appearance, regardless of the light. A surface that reflects all wavelengths equally appears white, whilst a surface that absorbs all wavelengths equally appears black. Sorry - I do signal processing for a living. . . <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> .bipartisan (bī-pär'tĭ-zən, -sən) [Adj.] Maintaining the ability to blame republications when your stimulus plan proves to be a devastating failure.IMPEACH OBAMA! </div>

MeteorWayne · Sep 11, 2007

Not sure I ever gave you my official welcome Andrenalynn. You seem like an interesting and educated person with some overlap with my experiences (25 years in the technical end of the TV biz) so here it is: Welcome!!!! <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

adrenalynn · Sep 11, 2007

Thanks! Our only intro to date was: I whined, you graciously responded, your response was summarily dismissed by factors outside of our control. <img src="/images/icons/wink.gif" /> I do appreciate both, though! Yes, we've probably been down similar roads. Although I started out in astrophysics, my "claim to fame" is primarily centered around perceptive video coding schemes, JND stuff, for optimization of "squirting the bird" in the broadcast space. With apologies for OTing the thread, I'll move this further into PM and your Aurigid thread I've been meaning to spam up with a photo. <img src="/images/icons/smile.gif" /> Thanks again! <div class="Discussion_UserSignature"> .bipartisan (bī-pär'tĭ-zən, -sən) [Adj.] Maintaining the ability to blame republications when your stimulus plan proves to be a devastating failure.IMPEACH OBAMA! </div>

MeteorWayne · Sep 11, 2007

Aha, sorry about that one. It was a cranky day <img src="/images/icons/smile.gif" /> We old f**ts are subject to that now and agin <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

adrenalynn · Sep 11, 2007

Nonono - *I* whined. You were gracious. You good. Me bad. And I represent that remark.

<img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> .bipartisan (bī-pär'tĭ-zən, -sən) [Adj.] Maintaining the ability to blame republications when your stimulus plan proves to be a devastating failure.IMPEACH OBAMA! </div>

emperor_of_localgroup · Sep 12, 2007

most people perceive something between 100,000 [ Mapping color perception to a physiological substrate Calkins, 1993, Visual Neurosciences] and 7 million [Myers, 1995, Psychology] distinct shades. Where did you get this!!!! Million shades? May be only in theory. Ordinary people practically can't tell the difference between even 256 shades of a color. That's why we used to have only 8-bit for colors in our computers. I myself can't even separate more than 16 shades. Anyway, let me recap what you all said. Photons of many wavelengths from the sun strike the rods and cones of our eyes and their combined effect is white color. There is no combination of photons before they strike our eyes? Is this right? Which is kind of strange because there are electric and magnetic fields associated with photons. And those fields supposed to interact. Origin of photons may be the reason why one photon doesn't interfere with another. Not sure. <div class="Discussion_UserSignature"> Earth is Boring </div>

primordial · Sep 17, 2007

Mr. Emperor ! You have a valid question. One can test this idea possibly by observing light that passes through the edge of a gravitational lensing, to see if the spectrum seperates as it does through glass. However Light has a phenomenonal atribute that's called the principle of duality, where light has both particle and wave atributes. If you test it as it as a particle it has the characteristics of a particle, if you test it as a wave it has the characteristics of a wave, so it depends how you test it.

adrenalynn · Sep 17, 2007

Sorry for the misunderstanding - that's distinct shades of color, not distinct shades of A color. My source was Psychology by David G. Myers. Worth Publishers, 1995. Pg 165. The exact quote was : "Our difference threshold for colors is so low that we can discriminate some 7 million different color variations." The low-end was from The Visual Neurosciences, Volume 1, MIT Press, 1993. I'll address your second question shortly. Just getting back into town... <div class="Discussion_UserSignature"> .bipartisan (bī-pär'tĭ-zən, -sən) [Adj.] Maintaining the ability to blame republications when your stimulus plan proves to be a devastating failure.IMPEACH OBAMA! </div>

siarad · Sep 18, 2007

Just one other point. The colours we perceive may not be the actual colours. Our colour vision has constant colour correction for noon-day sunlight, it's done by a mathematical calculation in three dimensions. Red sunsets are actually redder than we perceive due to this correction. Some partially colour blind people gain extra colour perception by wearing tinted glasses to help or fool this calculation. In films I've seen blue cars turn green & even a London Red bus turn blue due to entering a shadow. Lots of us must have seen green shadows caused by red light in pubs & clubs. All shadows are colourless but our constant colour correction adds the green to correct to noon-day sun. It's possible to show colour pictures simply by screening two monchrome images, I recall Professor Land, of Polaroid fame, showing these to cinema audiences in 1959 confounding people with colour cameras whose pictures showed the screen to be monochrome <img src="/images/icons/rolleyes.gif" />

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