Re: Spikes in the reflected spectrum

Thanks for the comments.  It is good to know that usually someone has been
thinking or doing the work that is in the same direction.  The spinning
idea seems to be a simple but effective way to test for reflection
addition.

The comments on the continuous spectrum also were helpful.  I hadn't
thought of the light being affected by thermal causes because I tended to
think in terms of the photon being generated by the electrons falling back
to a stable level in the atom.  But when you talked about thermal effects,
I started to think about the radiation given off by all objects which is
related to the temperature.  This is also a electromagnetic radiation. 
When one thinks about the atoms moving due to temperature (thermal)
conditions, and changing speeds due either collisions or just vibration, I
can see how the wavelength might be affected.  Is it similar to the dopler
effect?  Some atoms move away from the observer when the photon is emitted
while others are moving towards the observer when emitted.  If the movement
is fast enough, the wavelengths would be different. Maybe this is not
correct but at least your comments have helped explain the situation.

Erik

Danny Rich wrote:
> 
> "Erik Nikkanen" <[EMAIL PROTECTED]> wrote in message
> news:[EMAIL PROTECTED]
> > Hi Art,
> >
> > Thanks for the added information on material that either absorbs locally
> or
> > re-emits locally, to produce negative or positive spikes.  It is
> > interesting.  This talk about the electrons brings up another related
> > question that I do not really understand.
> >
> > As I understand it, a photon is the result of an electron collapsing from
> > an unstable level back to a specific stable level in the atom, which
> > implies a quantum amount.  I have been under the impression that the
> > wavelength is then related to a quantum amount between two . Maybe the
> > photon wavelength is also related to the energy the photon had before it
> > collapsed to that specific level from outside the atom.  Sorry, I know the
> > terms are not correct.
> >
> > Anyhow, I have wondered why natural light seems so continuous and not
> > broken up by descrete wavelengths related to some quantum values at the
> > origin.  I know they look at the EM energy from distant sources to
> > determine the materials at those sources.  These show up as spikes.  But
> > visible light seems to be mostly continuous.
> >
> > Can you straighten this out for me?
> >
> > Thanks.
> >
> > Erik
> >
> I will jump in at this point to drop my few cents worth.
> 
> First, on the original subject and the discussion about basis vectors.
> While 3 basis vectors will reproduce the tristimulus values reasonably well
> they only predict about 95% of the variability of the spectral curve.  Due
> to the nature of the color matching functions, most of this error
> accumulates in the ends of the spectrum and produces rather unnatural
> looking spectral signatures.  There is a better method based on the early
> work of Maxwell that uses reflective primaries.  It is the basis of  much of
> the work of Dorothy Nickerson at the USDA in the 40s and 50s.  It was
> adapted and commercialized in an instrument known as the VCS-10 (for Visual
> Color Simulator) and in the ColorCurve color selection system and the
> matching computation (as published by Dr. Chris Hawkyard of UMIST) in what
> eventually became the Colorite simulator.  This method uses light reflected
> from the primary materials (historically Munsell papers) and mixes it
> additively (usually by spinning the papers).  If you start with realistic,
> smooth reflectance curve then you can predict a realistic, smooth
> reflectance curve that matches any color with a chroma less than the
> primaries.  The system can use as few as 3 primaries or as many as 9.
> Adding more tristimulus values to the matching process reduces the
> metamerism.   For a clear description of the method you might try looking up
> ASTM E1541 on how to use the ColorCurve system.
> 
> In answer to your inquiry about Art's comments on the quantum chemistry of
> colorants  - if all of the atoms of every material were sitting perfectly
> still then we would observe only line spectra.  But random thermal motion
> results in collisions that broaden the absorption lines and most materials -
> especially solid materials - have a limited number of widely spaced
> absorption bands after which the bands get closer and closer together until
> there is only an infinitely small difference in energy from one band to the
> next.  The is often referred to as the continuum band and is the main cause
> of continous emission (blackbody radiations) and reflectance curves of
> yellows, oranges and red which appear to have 100nm wide absorption bands.
> They are really an infinite or nearly infinite series of discrete bands.
> 
> Danny Rich