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Main Question or Discussion Point
I want to know what exactly is the physical significance of absorptance versus absorbance. I have not come across a reference that clearly explains the distinction between the two quantities.
From the definitions:
When light is incident on a material, by finding the fraction that gets reflected and transmitted, we can find the absorptance — the fraction that is absorbed:
$$\underbrace{R}_{\text{reflectance}}+\underbrace{A}_{\text{absorptance}}+\underbrace{T}_{\text{transmittance}}=1$$
Absorbance (also called optical density) follows from the BeerLambert law and is written:
$$\text{Absorbance}=\log_{10}\left(1/T\right)$$
For a given sample, I used a spectrophotometer to find both quantities. But the curves appear to give contradicting information about my sample:
Here is the problem:
The absorptance curve above shows that in the red (~680 nm) and in the blueviolet (<450 nm) regions we have approximately the same level of absorption. But the absorbance curve shows that the absorption is much greater in the blueviolet than in the red. These can't both be true.
I believe that these quantities are providing different information about the sample. But what exactly is the difference?
Any explanation would be greatly appreciated.
From the definitions:
When light is incident on a material, by finding the fraction that gets reflected and transmitted, we can find the absorptance — the fraction that is absorbed:
$$\underbrace{R}_{\text{reflectance}}+\underbrace{A}_{\text{absorptance}}+\underbrace{T}_{\text{transmittance}}=1$$
Absorbance (also called optical density) follows from the BeerLambert law and is written:
$$\text{Absorbance}=\log_{10}\left(1/T\right)$$
For a given sample, I used a spectrophotometer to find both quantities. But the curves appear to give contradicting information about my sample:
Here is the problem:
The absorptance curve above shows that in the red (~680 nm) and in the blueviolet (<450 nm) regions we have approximately the same level of absorption. But the absorbance curve shows that the absorption is much greater in the blueviolet than in the red. These can't both be true.
I believe that these quantities are providing different information about the sample. But what exactly is the difference?
Any explanation would be greatly appreciated.
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