What is Light?

Georg R. Baumann · Jun 15, 2007

I was thinking this might be of interest to some people. At the end, as photographers, we are "Light-Hunters" <grins> and as such it might help to know a little more about what we really are after. While we still do not know what Light really is, we can describe it as a wave-particle duality. Light has a dual nature; in some cases it behaves as a wave, and in other cases it behaves as a particle. The name of the particle associated to light is called a photon. A photon itself has no mass, and interesting enough, it only exists at lightspeed, if you slow it down, it does not exists anymore. <grins> Research on photons has been undertaken in massive ring accelerators enabling fundamental physics research:

http://zms.desy.de/press/background_information/research_with_photons/index_eng.html

The worlds largest particle ring accelerator the LHC, large Hadron Collidor is CERN, CERN stands for European Center for Nuclear Research, a tunnel which has a circumference of 27 km and is buried 100 meters beneath the Franco-Swiss border. It is composed of 1700 large magnets and it also includes a significant quantity of corrective magnets and requires the largest cryogenic infrastructure ever created using superfluid helium at -271°C, a temperature lower than that of interstellar space.

http://public.web.cern.ch/Public/Welcome.html

On a side note, without CERN we would not have the World Wide Web today, a significant achievement in deed:

http://public.web.cern.ch/Public/Content/Chapters/AboutCERN/Achievements/WorldWideWeb/WWW-en.html

And of course there is ATLAS:

http://atlas.ch/

But what is Light?

NASA: Dr. Sten Odenwald:

What is light; how does it travel; and how the ding dang do you measure its speed?
Physicists tend to be very pragmatic folks when it comes to certain things. If you have a theory such as quantum mechanics that works, you don't spend much time asking what it all means, you just follow what the experiments and mathematics are telling you is 'out there' and you leave such big questions for the 21st Century philosophers to ponder.

The speed of light was measured by Danish astronomer Ole Roemer back in 1675. He noticed that the predicted transits of Jupiter by its satellites would come over an hour after they were scheduled, and concluded that this was because light took time to get from Jupiter to earth. SInce the distance to Jupiter was known, it was a simple matter to divide this by the delay time to get the velocity of light pretty accurately. Today, thanks to high speed electronics, you can measure time intervals to nanoseconds, during which time light travels about a foot or so.

As for what light is of itself, the answer depends on whether you which to speak the language ot particles or waves. Both are equivalent and self consistent, but I prefer the particle description to guide my feeble intuition.

Light is composed of particles called photons. Each photon is a discrete packet of electromagnetic energy which travels at, what else, the speed of light. The packets carry no mass, but they do have an effective mass that is determined by the energy they carry compliments of Einstein's famous E = mc2. The amount of energy that each photon carries is determined by its size, which in the wave description, is just the wavelength of the light wave. Each quantum can be thought of as one complete oscillation of the electromagnetic wave. Specifically E = hc/wavelength where h is Planck's constant and c is the velocity of light.

Exactly what is light, we don't really know other than in the quantitative details of the above description. The above description IS what light is, just as the detailed description of a dog is what a dog is.

How does light move? During the last century, it was pretty well believed that light was a wave phenomenon that needed a medium... the ether...in order to propagate from one place to another. It was thought of as some odd kind of water wave. Then a series of famous experiments proved that the ether didn't exist, so physicists had to re-think what the essential nature of light was. The best understanding we have is that it is a disturbance in the electromagnetic fields of charged bodies. When you look at the electric field of a stationary charge, its lines of electrostatic force are directed radially away from the charge into space. These fields are dynamic things which travel at the speed of light. Now, if you accelerate this charge, the geometry of the field changes, and the information about where the new field is located in space travels outwards as a kink in the electromagnetic field. This happens because a change in the electric field generates a changing magnetic field which then generates a changing electric field and so on out into space at the velocity of light. This is what Maxwell discovered in his famous wave equation for the electromagnetic field. Light is, essentially, a self-propagating pulse of information that tells us that the state of some electromagnetic field has been altered somewhere in space.

If you prefer the quantum description of photon 'bullets' being ejected into space at light speed, that's fine too. Isn't physics grand?

Next I came across a great site that might be of interest for parents in need of some educational material:

http://www.opticalres.com/optics_for_kids/kidoptx_p1.html

And last not least the more scientific outlook in three sections:

Classical view
http://www.fnal.gov/pub/inquiring/more/light/light_page1.html

Relativistic view
http://www.fnal.gov/pub/inquiring/more/light/light_page11.html

Quantum physics view
http://www.fnal.gov/pub/inquiring/more/light/light_page27.html

Georg R. Baumann · Jun 15, 2007

Some fascinating photos from ATLAS:

http://atlas.ch/atlas_photos.html

Asher Kelman · Jul 1, 2007

What is light?

For humans it's a feature of the universe that allows us to know what's happening around us. It is what provides the information to our eyes. So we know better how to navigate and exploit the environment.

From that, light becomes a metaphor for understanding. The latter is the most important meaning and definition to me.

Asher

Doug Kerr · Jul 3, 2007

Light in the head

1. Electromagnetic radiation in the visible band, or (by extension), in adjacent bands (e.g., IR light, UV light).

2. The opposite of heavy (adj.).

3. The opposite of dark (adj.)

4. Fire put to a cigarette, etc.

5. A lamp ("put a light in the window")

6. A lighthouse

Next week: The meaning of meaning.

Don Lashier · Jul 3, 2007

Light is the bridge between mind and matter, between spiritual and physical - light is the neuro-transmitter of the cosmic consciousness.

There

- DL

Maris Rusis · Jul 5, 2007

Light is also the form in which energy escapes from photographic subject matter. Before this energy escapes it is an integral component of the subject and is responsible for some of its properties.

Escaping light is something that was part of the subject matter, that can be spatially organised by a lens, and which can burrow into a sensitive surface to occasion marks which constitute a picture of the original subject matter. Wow!

The only energy needed to make a photograph comes entirely from the subject matter. The picture making marks that give a photograph visible form are generated entirely by the internal chemical potential energy of the sensitive materials.

Remember that photography was invented in and works perfectly in a world without electric power, information technology, or data processing of any kind.

David Sommars · Mar 31, 2009

Also interesting to note that a RED door is actually not RED at all. Its really every color except red.

The unseen is more "Real" then the seen so many times.

Asher Kelman · Mar 31, 2009

The nice thing about the red door is that it gives back that red and doesn't keep it like the other colors.

Asher

Andy brown · Mar 31, 2009

Yep!
Light's cool.
Light is also the thing that stands to save us from ourselves.

All those photons(?) people, beaming down on us, powering the Earth for millenia.

Go solar!

Sorry, I'm kinda passionate about this.
I'm in the industry and in an area( south eastern Australia which is embracing the challenge and beating its targets to be 50% renewable energy by 2020.

Massive Solar movement taking off here.

Oh yeah, and it's good for photos!

Asher Kelman · Mar 31, 2009

Andy brown said:
Sorry, I'm kinda passionate about this.
I'm in the industry and in an area( south eastern Australia which is embracing the challenge and beating its targets to be 50% renewable energy by 2020.

Massive Solar movement taking off here.

Oh yeah, and it's good for photos!

Yes, Andy,

But it must be made beautifully!

I'd love to see sculptural forms not ugly add-ons every where!

Asher

David Sommars · Mar 31, 2009

Asher Kelman said:
The nice thing about the red door is that it gives back that red and doesn't keep it like the other colors.

Asher

Yes, it is.

The interesting thing is the reflectivity knowledge can help when we think of structures that we photograph as not JUST 2D surfaces that contain color, but more like transponders beaming information to us, and that information can be intercepted slightly differently depending on our distance, and things in-between us and them,

The super interesting thing is that they are like translators, the light has to come from somewhere else. That pushes us to understand light quality not quantity. etc etc.... Its really a blessing in disguise that its not as simple as first glance. If we really want to understand in depth, we will always be awarded.

Maris Rusis · Apr 1, 2009

The structures that we photograph are, in a sense transponders, because they send us stuff from which we are able to distill information. But they do more.

People tend to underestimate the physicality of the photographic event. At the moment of exposure film actually gets heavier. The extra heaviness, the extra MASS, comes from the subject matter which gets lighter by the same amount. In the real world the electromagnetic field that suffuses the subject matter replaces the lost mass very quickly and no one notices.

Most of the stuff that subject matter sends through the lens and into the film gets converted into heat which leaks away but some remains. A film bearing a latent image is heavier than an unexposed film.

How much heavier? I don't know how to type scientific notation in this web format but in words:

"A sheet of 8x10 ISO 100 film receiving middling exposure gains about 10 to the minus 23 kilograms at the moment of exposure. Assuming a quantum efficiency of 1% for this film the residual latent image contributes about 10 to the minus 25 kilograms as gained mass."

One could imagine that these masses are so small that to be hit by them would causes no sensation in the human body. Not so! Remember light has a "muzzle velocity" of 300 000 km/sec so it packs a punch. If you replace the film in a camera with your own eye and fire the shutter you sure see something.

The generation of pictures in situ in a sensitive surface by the impact of stuff that used to be part of the subject matter makes photography fundamentally different from painting or drawing.

David Sommars · Apr 1, 2009

Maris Rusis said:
The structures that we photograph are, in a sense transponders, because they send us stuff from which we are able to distill information. But they do more.

People tend to underestimate the physicality of the photographic event. At the moment of exposure film actually gets heavier. The extra heaviness, the extra MASS, comes from the subject matter which gets lighter by the same amount. In the real world the electromagnetic field that suffuses the subject matter replaces the lost mass very quickly and no one notices.

Most of the stuff that subject matter sends through the lens and into the film gets converted into heat which leaks away but some remains. A film bearing a latent image is heavier than an unexposed film.

How much heavier? I don't know how to type scientific notation in this web format but in words:

"A sheet of 8x10 ISO 100 film receiving middling exposure gains about 10 to the minus 23 kilograms at the moment of exposure. Assuming a quantum efficiency of 1% for this film the residual latent image contributes about 10 to the minus 25 kilograms as gained mass."

One could imagine that these masses are so small that to be hit by them would causes no sensation in the human body. Not so! Remember light has a "muzzle velocity" of 300 000 km/sec so it packs a punch. If you replace the film in a camera with your own eye and fire the shutter you sure see something.

The generation of pictures in situ in a sensitive surface by the impact of stuff that used to be part of the subject matter makes photography fundamentally different from painting or drawing.

What If I take a picture of undeveloped film ?

Just kidding, I guess Im with you on the first part, BUT I dont shoot with film anymore, also I dont understand the last part, how can we ascertain the subject matter gets lighter ? Do you mean the light, or the actual structure were shooting ? Just curious cause, Im slow be nice !!! LOL

Doug Kerr · Apr 1, 2009

Hi, Maris,

Maris Rusis said:
The structures that we photograph are, in a sense transponders, because they send us stuff from which we are able to distill information. But they do more.

People tend to underestimate the physicality of the photographic event. At the moment of exposure film actually gets heavier. The extra heaviness, the extra MASS, comes from the subject matter which gets lighter by the same amount. In the real world the electromagnetic field that suffuses the subject matter replaces the lost mass very quickly and no one notices.

Most of the stuff that subject matter sends through the lens and into the film gets converted into heat which leaks away but some remains. A film bearing a latent image is heavier than an unexposed film.

How much heavier? I don't know how to type scientific notation in this web format

One way is using the "programming" notation: "1E-23" kg for the first number you mention below. Another convention is "10^-23 kg".

"A sheet of 8x10 ISO 100 film receiving middling exposure gains about 10 to the minus 23 kilograms at the moment of exposure.

Interesting to note. Comes from m= e/(C^2); that is, from e=mC^2.

Best regards,

Doug

Doug Kerr · Apr 1, 2009

Hi, David,

David Sommars said:
Do you mean the light, or the actual structure were shooting ?

I think the intimation is that the subject becomes lighter. But that's probably actually not so really with respect to objects photographed by reflected light.

An object that emits photons becomes lighter (each photon that departs carries with it a certain amount of energy, which comes from part of the object's mass). But an object photographed by reflected light doesn't emit many (some, depending on its temperature), but rather "reflects" them. (It is thus the sun, for example, that loses mass in the process!)

Best regards,

Doug

fahim mohammed · Apr 2, 2009

1. Not heavy

2. Understanding

question: what is a registrant?

Asher Kelman · Apr 2, 2009

Registrant? That's a person who has in the past been active, but now is not.

Asher

Clayton Lofgren · Apr 2, 2009

Does this mean that if I use a motor drive and take a few million shots of my wife that I won´t have to spring for a tummy tuck?

Asher Kelman · Apr 2, 2009

Clayton Lofgren said:
Does this mean that if I use a motor drive and take a few million shots of my wife that I won´t have to spring for a tummy tuck?

Clayton,

That's dangerous! You will fall in love with your wife's pictures and become light-headed and then go into convulsions. Your poor wife will be widowed, even though you are alive. She'll watch you, but you'll be twitching, eyes rolling, as you constantly roam through her pictures grading and re-grading where she is most beautiful.

Also forget the tummy tuck! A larger size suit is best!

Asher

Clayton Lofgren · Apr 3, 2009

I had never planned on developing the film.

Andy brown · Apr 3, 2009

Clayton Lofgren said:
I had never planned on developing the film.

I love this. Weight loss while you sleep ( tripod and motordrive).

Asher, back to your comment sunshine ( pun intentional), what did you mean about the add ons? Did you mean solar panels? Do you find them ugly? I wasn't quite sure what you meant.

p.s Hope I'm not derailing the thread, just going a little bit tangential for a moment.

Asher Kelman · Apr 3, 2009

Andy brown said:
Asher, back to your comment sunshine ( pun intentional), what did you mean about the add ons? Did you mean solar panels? Do you find them ugly? I wasn't quite sure what you meant.

p.s Hope I'm not derailing the thread, just going a little bit tangential for a moment.

Yes, we are tangential, but so are solar panels!

When they are added to a building as after thoughts they don't fit in with the lines of the original architecture and so are just clutter and untidy. Ideally, solar would be built into the contours of roofs.

Asher

Andy brown · Apr 4, 2009

Asher Kelman said:
Ideally, solar would be built into the contours of roofs.

Asher

Sure, and that's probably not far away.
When I see a solar array though my mind skips to The Latrobe valley ( the area a few hours from here where coal is mined and burned to produce electricity) and I visualise just a bit less dirty brown smoke belching and it's a pretty thought.
And the PV panels themselves are certainly not ugly.

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