Options
Theory question: Viewing coins with different light sourses...
dan1ecu
Posts: 1,573
Greetings, All -
A coin will appear differently if viewed under sunlight as opposed to fluorescent light.
Sunlight is a continuous spectrum of wavelengths, whereas fluorescent light produces a "line spectrum" - i.e., only certain wavelengths of light are present. Halogen lamps also produce line spectra as opposed to continuous spectra.
Has anyone looked into why the different types of light make coins appear differently? Are there theories that go into wavelengths, frequencies, and energy of light? Are there theories that involve how our eyes perceive various colors?
What's the best theory you've heard that explains why a coin's appearance depends on the type of light that is used to view it?
Dan
A coin will appear differently if viewed under sunlight as opposed to fluorescent light.
Sunlight is a continuous spectrum of wavelengths, whereas fluorescent light produces a "line spectrum" - i.e., only certain wavelengths of light are present. Halogen lamps also produce line spectra as opposed to continuous spectra.
Has anyone looked into why the different types of light make coins appear differently? Are there theories that go into wavelengths, frequencies, and energy of light? Are there theories that involve how our eyes perceive various colors?
What's the best theory you've heard that explains why a coin's appearance depends on the type of light that is used to view it?
Dan
0
Comments
try looking at coins through a polarized glass sometime under different lighting conditions.
K S
color and nature of the surface of the coin affects how it will be seen. The depth of the
marking and angle of the light play critical rolls. The nature of our eyes and how the
brain interprets information is really a determining factor in what is seen. Learning
plays a vital role in sight and an experienced collector won't see the same thing as a
novice.
Florescent light confounds what collectors are trying to see on a coin because it does
not act as a single source as do most light sources. The light is coming from a wide bulb
which is usually constitutes a wide lighting angle. For most individuals it is best to use
the same light or few lights each time for examining coins and this is generally an incan-
descent light.
Morgan Dollar Aficionado & Vammer
Current Set: Morgan Hit List 40 VAM Set
Like you said, certain light sources produce various different wavelengths of light. Sunlight produces all wavelenghts in the visible spectrum, from .3 to .7 microns. I dont know what various other sources produce but I am sure that you could look it up on the internet.
What makes these coins appear differently under different lights is the lights constituents as described above. If a light source contains only the lower wavelength bands (i.e. the reds and oranges), there is no way that the coin will appear blue to your eye or a photograph that you take of it.
Now of course, the coin will not appear blue (even under pure white light) unless the oxidation present on it is comprised of materials that reflect blue photons or emit blue photons.
That is the theory to understand. Simply, light, when it encounters an object is either scattered (reflected) or absorbed. The amount that an object scatters an individual wavelength of light is quatified as its albedo or also as its percentage of being a perfect blackbody. A perfect blackbody will completely absorb all of the light for an individual wavelength that it encounters. An object that absorbs 20% of a wavelength scatters 80% of it and has an 80% albedo. Also see Planck's Law
As far as we know in science there is no such thing as a perfect blackbody. I digress....
Oxidation on a coin does not absorb really any light of any color. It scatters all of the light that it encounters. The reason that we know this is that you cant see a coin in the dark!!! If a coin with blue toning did anything other than scatter blue wavelengths, when we took it into a dark room it would glow blue!!! And unless you have some freaky coins, they wont do that!!
A coin does however absorb alot of infrared light (about .8-10 micons). If you left a coin in the hot sun for instance and took it into a dark room and put on your Infrared goggles, you could see it!! Understand the diffference?
Anyway, back to coins and light sources.
Since certain light sources that we view coins with possess different amounts of individual wavelengths they will appear differently under each with a certain set of guidelines.
In order for a coin to appear a certain color, it must both be viewed with a light source that has that wavelength of light AND must possess oxidation/toning of a kind that is a very stong scatterer of an individual wavelength color.
That is just color. Intensity (aka Power) is also very important as to how the coin appears to your eye. That is intuitive of course. Angle will have an effect which is why a coin cartwheels.
If you want to learn more about why we see what we do, check out additional scattering topics/regimes like Rayleigh scattering, Mie scattering or geometric optics.
Those will help explain lots of questions that most people cannot explain themselves. Insert here your little daughter asking "Daddy, why is the sky blue?"
or "Why is the sun orange at sunset and yellow during the day?".... Very neat stuff. Feel free to ask more questions but I will stop now before everyone figures out that I am a geek!!
John
siliconvalleycoins.com
I think that's also how the reveal bulb works. Seems like it's shifted a bit toward red. That's just my guess.
For a camera I would think that the camera would have the best detail when taking pics in blue light because blue is higher frequency and a shorter wavelength, that is providing that it's frequency response to light is equal across the spectrum. I believe that finer details can be made out with shorter wavelength light. That's why they have been pushing lasers for DVD and such toward the blue end of the spectrum so that they can pack more data on a disk.
That difference always made me wonder if the reveal bulb actually does anything useful in taking pictures. It may make the details sharper to the eye, but may not do the same thing for a camera.
If anybody has better info, please step in.
I think you have it backwards... blue has the longest wavelength, shortest frequency...
The only way I keep that straight is the whole sky being blue thing.
Most of our atmosphere has very small aerosol particles that fall into the Rayleigh scattering regime. The rayleigh regime scatters light as a function of wavelength to the fourth power. In other words, it scatters the higher wavelength light much better than the low. Blue is the highest, is scattered better, and therefore we have a blue sky!!
Now that I think of it, I think that I put the above post for infrared in the wrong micron range...
As far as the biologics, never heard about the receptors but it sure sounds interesting...
siliconvalleycoins.com
1) Coin Grading by visual observation is best done with a harsh point-light source like either incandescent or halogen bulb because it more clearly shows the hairlines and other flaws on the coin which are critical to establish its grade.
2) However, Coin Photography by optical or digital camera is very dependent on color balance of the light which you can effect by either changing the type of light source (color determined by filament/source type and temperature), the film type in film camera, or by adjusting the digital color balance for a digital camera.
CL: I think that MGoodM3 has it correct. Blue light is of a higher frequency and shorter wavelength -- that's why sunsets are more red than blue...
Stuart
Collect 18th & 19th Century US Type Coins, Silver Dollars, $20 Gold Double Eagles and World Crowns & Talers with High Eye Appeal
"Luck is what happens when Preparation meets Opportunity"
You summed it up nicely. The only comment I'll add is how "Blue-blockers" work. The eye, like any optical system, is not perfect. There is a lot of chromatic aberration in the eye. What does this mean? Think of the visible optical spectrum - red is at one end, yellow-green in the middle, and blue at the other end. Suppose sunlight (full spectrum) is in perfect focus. The yellow green is in perfect focus, that is, it comes to a point on the retina. Red will focus behind the retina, and blue will focus in front of the retina, both being out of focus. When using blue-blockers, the visible spectrum is filtered and narrowed. The object viewed contains less of the visible spectrum, and causes less chromatic aberration, therefore, appears to be sharper.
One would get a similar effect with "red-blockers" if they existed.
Coinlt.,
Mark is correct. Blue does have a shorter wavelength. The sky looks blue because the shorter wavelength scatters more.
I must have got my Rayleigh regime wrong... I could have sworn that Rayleigh scattering was a function of lambda to the fourth power...
I had the right concept, just the wrong side of the spectrum...
Forgive me... I am deep into my acoustics thesis now... and have thrown all of that "above water" crap out of my head....
John
siliconvalleycoins.com
1/ lambda to the fourth power... That makes a teeny bit of a difference...
CL: I think that MGoodM3 has it correct. Blue light is of a higher frequency and shorter wavelength -- that's why sunsets are more red than blue...
That is the main part of it but....... At sunset, the light has to go through a much thicker chunk of the atmosphere (the limb). The blue light has to go through so much atmosphere that all of the blue light gets scattered...leaving only the longer wavelengths...
J
siliconvalleycoins.com
K S