Talk:Absorbance

Wiki Education Foundation-supported course assignment

This article is or was the subject of a Wiki Education Foundation-supported course assignment. Further details are available on the course page. Student editor(s): Andrew.Tang88. Peer reviewers: Andrew.Tang88, Vicky.mai36.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 13:17, 16 January 2022 (UTC)

Natural log or log base 10

"Outside the field of analytical chemistry, the absorbance is sometimes defined as the natural logarithm instead of the base-10 logarithm." is what is said in the article, but I cannot figure out if that means the logarithm depicted is base 10 or the natural logarithm. Logically, I don't see how 10 could appear in the nature of light and absorbance, so I think that it is the natural logarithm. I am going to change it to LN, but if thats not right, somebody correct me. —Preceding unsigned comment added by EulerGamma (talk • contribs)

I'm under the impression that the reason it is converted to a logarith, is so the numbers are easier to work with. The choice of of a natural log or a base 10 log would be determined by whether you prefer for work in powers of 10 or powers of e, and not based on any phsyical property of light. I think it makes more sense to express is as a log base 10 in this article, since the other articles relating to this one (optical density and transmittance) use log base 10.

--Justin —Preceding unsigned comment added by 128.174.75.226 (talk • contribs)

It's converted to Log because of the Beer-Lambert Law. The log is directly related to concentration. Also the absorbance is often reported as optical density or OD as the unit. The Log should be base 10 because that is the most common use. Clearly the choice of base is otherwise arbitrary.

Analytical chemistry and engineering applications generally use decadic absorbance. Within physics, astronomy, and molecular spectroscopy naperian logarithms are usually seen, but the term "absorbance" isn't necessarily used. IUPAC has dealt with this discrepancy in its Gold Book and other publications. When in doubt, one should always specify naperian or decadic. 128.146.32.223 (talk) 01:25, 2 September 2009 (UTC)

Simpleminded illustration

Heat absorbed on the sunny side of the black tire causes the snow to melt faster on that side.

I was wondering if a less technical aspect could be visualized with an photo like this? For the non-mathematical oriented reader. I am biased as I am the creator of the photo. Opinions? --Slaunger (talk) 23:35, 2 December 2010 (UTC)

It's a pretty picture. In my opinion, it helps to illustrate the concept, "things get warmer when they absorb light". I don't think that's a concept that's important for this article. Maybe a different article (thermal radiation?) Then again, I think that concept would be better illustrated by pointing out the temperature difference between the equator and Antarctica, or between summer and winter, or between Mercury and Pluto. The difference between the sunny and shady sides of a tire is a pretty small difference, and people might get the wrong impression that this is not a very important concept. :-) --Steve (talk) 23:53, 2 December 2010 (UTC)

Acknowledged. Also the effect on the photo is perhaps not sufficiently clear to make the point clearly. At the second tire it is not as clear. But thanks for taking your time to consider it. --Slaunger (talk) 10:17, 3 December 2010 (UTC)

% column

Anyone can multiply .79 by 100 and see that it is 79. Shouldn't we take out that useless third column (% Transmittance) from the table? —Preceding unsigned comment added by 129.22.53.144 (talk) 08:36, 18 April 2011 (UTC)

I put it back...it's obvious to you and me that 0.001 is 0.1%, but some people find "0.1%" easier to understand at a glance. Also, spectrometers often output "percent transmission" but just call it "Transmission", and this can lead to confusion, but the confusion is alleviated when someone sees both columns in this article and thereby becomes aware that both "fraction" and "percent" are commonly used in this measurement. Anyway, what harm is it doing? It's not a huge deal either way, but I like it so I put it back in :-) You're welcome to take it out yet again if you feel strongly. --Steve (talk) 23:48, 18 April 2011 (UTC)

Absorptance

The two links for Color and Vision Research Laboratories are no longer valid. Can someone find current link on that site or from others that still verify this info? (Skoot13 (talk) 15:34, 13 April 2012 (UTC))

Definition

In the very first line of the article "radiation falling upon a material, to the radiation transmitted through a material." there is a patently false statement. The reference is to "Webster's" but Webster's says (correctly) for physics "The ratio of the radiation absorbed by a surface to the total energy falling on that surface described as a percentage"

A definition of absorbance cannot be based only on incident and transmitted energy. This methode of definition would require reference to reflection (reflectance).

The full Webster's definition for absorbance is "A measure of the rate of decrease in the intensity of electromagnetic radiation (as light) as it passes through a given substance; the fraction of incident radiant energy absorbed per unit mass or thickness of an absorber"

Often in properly arranged measurements (typically using a cuvette as show in figure 1)and for nonscattering samples, reflection is ignored. However it is not possible to ignore it in a general definition. Take for example silver which typically has very low absorbance at any thickness even when %T is negligible. Bubsir (talk) 14:24, 17 April 2012 (UTC)

Webster's is not a good source for scientific definitions -- just try looking up a few random ones -- and should be removed. A textbook or something like that would be much better.

It would indeed be strange for the word "absorbance" to describe a mixture of absorption and reflection. But that does not necessarily mean that it is not true. I'm trying to find a source that discusses whether a proper measurement of absorbance needs to be corrected for reflection, or alternatively, needs to not be corrected for reflection. (It is also possible that both these definitions are in use.) This source kind of implies the latter definition but in an indirect way. This source explicitly supports the former. Unless someone can find other references, I agree with Bubsir's proposed change of the definition. --Steve (talk) 21:11, 17 April 2012 (UTC)

Modifying Definitions and adding a history perspective

As I understand it, this article was a result of a WikiProject. As there was some discussion of definition of absorbance, I led with definitions (there are two) from the "Gold Book". I added the Background sections because the mathematics centered on Optics, while the use of the term "absorbance" is probably most prominent in spectroscopy. I'm guessing that the word is used many times in Wikipedia in articles that I did not find. I hope someone will join in helping referencing this in the other articles.

Using the Term "Optical Density" to Describe Absorbance

I'm currently editing a college lab manual, and trying to determine whether the term "Optical Density" is suitable to describe absorbance (in the context of measuring DNA concentrations using a spectrophotometer, i.e., absorbance at a specific wavelength over a fixed distance). This page has been the only source I could find to suggest that it is not appropriate to use the term "Optical Density". However, it only says such use "is discouraged" without a source to who may be discouraging it, and why. Would it be appropriate to include further discussion on why it is discouraged or a source for such discouragement? Or would it be appropriate to remove the comment until a source can be found?

For context, I have found this page and this page from manufacturers of plate readers that use the terms essentially interchangeably Thefezzident (talk) 22:58, 28 July 2023 (UTC)