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Properties of Light

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posted on Sep, 16 2005 @ 12:02 PM
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Recently I've started messing around with various 3D modeling software, and no matter what I do I can't get the lighting right. In all the reference material I've seen online, tutorials on lighting and whatnot, modeling realistic lighting in an efficient manner is one of the most difficult aspects in creating a software 3D renderer, due to the lack of understanding on how light interacts with various materials.

Now while I don't doubt that these people have done extensive research into this subject, my understanding is that the properties of light--specifically reflection and refraction--are not that mysterious. I know that, under a microscope, virtually every surface is extremely rough and jagged. The more rough a surface is, the less light is reflected and therefore the surface appears dull. The smoother the surface is, the more light is reflected and the surface appears polished and shiny.

I hope that's enough background on why I'm asking and what I already know. I do have a couple of questions with this, and if there's enough interest in the problem I'll probably ask a few more.

The main question I'm asking is how exactly are the physics of light calculated? I mean, when I turn on a light bulb, the light goes out in all directions of course. Is there anyway I can calculate the number of photons being sent out in a given timeframe (ie per second, millisecond, etc.)? If I understand correctly, the number of photons being sent out determines the "brightness" of the light bulb. What property of the photons determines the color of the light?

I guess that's as good a starting point as any. If I'm not explaining the problem or the questions well enough, feel free to ask.




posted on Sep, 16 2005 @ 01:28 PM
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Yes..I'm sorry i just wrote a huge explanation and went to hit post and it gave me error so when i pushed back button it erased all...


basically, your light bulbs or whatever operate at a specific amount of power in watts.... Joules / second

You can figure out the amount of energy within a photon by multiplying Planck's Constant by the frequency of the light. Those units will cancel out and you will left with energy in amount of Joules.

Take the amount of power the system is working in, in watts... divide by the energy within photons.

(Joules/second) / (Joules) = number of photons relased per second!



posted on Sep, 16 2005 @ 01:36 PM
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Originally posted by Aether
Yes..I'm sorry i just wrote a huge explanation and went to hit post and it gave me error so when i pushed back button it erased all...



I know exactly what you mean--done it myself many times. I'd recommend copying any post you've spent any amount of time on into notepad before clicking the Post button just in case that happens.

Just to clarify, the frequency of the light is figured based on its color, correct? I mean, red light has a much lower frequency than blue light, right?



posted on Sep, 16 2005 @ 01:43 PM
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ROYGBIV!

Wavelength Larger >>>>>>Smaller
Frequency Smaller>>>>>>Larger

It really makes sense because you can look at a blue flame and know it is hotter than a red flame. The amount of energy produced per sec is increased because you have more cycles per that same amount of time!



posted on Sep, 16 2005 @ 01:48 PM
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Okay, thanks Aether, I appreciate it so far.

How about this: knowing how many photons per second are being emitted from a light source the energy of each individual photon, the angle the photons are traveling to an object, and the distance to an object, how can I determine the amount/strength of light that hits the surface of that object?



posted on Sep, 17 2005 @ 11:02 AM
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Originally posted by MCory1
Is there anyway I can calculate the number of photons being sent out in a given timeframe (ie per second, millisecond, etc.)?

For an ordinary bulb, non TL, you need to know what temperature the glow spiral has, from that you can find in literature the blackbody spectrum and average wavelength lambda. Transform the average wavelength lambda into the average frequency nu according to c = lambda*nu, with c the speed of light. Since the energy of a photon is E = h*nu, and knowing the power P (power = energy per amount of time) consumption of your light bulb, you can calculate the average number of photons n per unit of time as n = P / E. I hope this is a correct approach, not sure. For TL lamps, I wouldn't know.



Originally posted by MCory1
If I understand correctly, the number of photons being sent out determines the "brightness" of the light bulb. What property of the photons determines the color of the light?

The wavelength distribution.



posted on Sep, 17 2005 @ 11:08 AM
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Originally posted by MCory1
How about this: knowing how many photons per second are being emitted from a light source the energy of each individual photon, the angle the photons are traveling to an object, and the distance to an object, how can I determine the amount/strength of light that hits the surface of that object?

That involves calculating flux integrals.



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