There are two main values that can be used to generally describe the absorption within a material. One is absorbance, and the other is absorptance.

Absorbance is defined as the logarithmic ratio of the intensity of the light incident on your sample (I0) to the intensity of the light passing through your sample (I). In chemistry, typically log10 is used, whereas in other fields (biology, etc.), typically ln is used. The equation is:

A = log10(I0/I) =  -log10(I/I0) = -log10(T)

where T is the fractional transmittance through the sample.

Absorptance is defined as the fraction of incident electromagnetic power absorbed by the material. It can be calculated from the simple RATS equation:

R + A + T + S = 1

where R is the reflectance, A is the absorptance (not to be confused with the "A" used for absorbance, which typically uses the same symbol), T is the transmittance, and S is the scattering from the material. All of these values are fractional.

Thus, if you are reading an absolute value of the "absorptance" from the Perkin-Elmer (with values of ~1.2 or 4.5), you are likely reading the absorbance. To obtain the fractional value, the true absorptance, you can apply the following equation:

%A = 100% - %T - %R -%S

Most of the time, you can assume that %S is negligible, but to obtain a true value of the absorbance of your sample, you would need both %T and %R measurements.

Note that if you assume %R is also negligible, then if you calculate %A = 100% - %T, the value you obtain should be identical to the value you get if you convert the "A" obtained from the Perkin Elmer (let's call it APE) to absorptance:

%A = 100% - %T = (1 - 10-APE ) * 100%

Hope this helps!

Sources: Andor.com "Absorption / Transmission / Reflection Spectroscopy" and Wikipedia ("Absorptance" and "Absorbance").

Absorptance could NOT be measured in %. Try to think about definition of absorptance. Absorptance is proportional to optical depth of the media, which can be from 0 to infinit.

Absorbtion can be characterized in percentage as 100% - T%. But relation to optical depth would be more complex.

Thanks Andrei..that is what I am stucking..I am measuring the absorptance of the coating on a glass material..and I can not measure the optical depth...so what should I do???and I have also related the absorption and absorptance..It is nothing but a difference of Log..still getting the concept also I am not able to get the exact result.

Dear Atasi,

first thought a typing error because never heard about absorptance. but found the following definition

A measure of the ability of an object to absorb radiation, equal to the ratio of the absorbed radiant flux to the incident flux.

Then in percentage this should be 1 - %T. If you want to correct for glass material you will have to recalculate the data from corrected absorbance to know %T of only the coating.

Thank you very much Titus for your answer.I will check it...But I am using instrument named perkin elmer.There I can get the value of transmittance, reflectance but not absorptance..If I substitute 100-(R+T), the value which are coming are not expected.

and Titus, I am facing a lot of problems regarding the particle dispersion.I need to discuss with you..I need to disperse copper oxide and aluminium oxide particles.What is the exact way ??

As said correction for the glass can only be made based on absorbance because only this is additive.

@Titus Sobisch

usually I use the term absorbance but absorptance is used as well

http://en.wikipedia.org/wiki/Absorbance

@Atasi Dan

It seems I do not understand the question. I have not ever use the particular instrument but I believe that knowledge of the concept should helps.

http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law

Absorbance (A) actually is the optical depth.

Value 100 - (R+T) looks very strange to me... A=-ln(T) or A=ln(1/T)

(I would use ln instead of Log or lg)

Reflectance should be accounted for T evaluation.

100% (I_0) is the light coming to the detector without absorption but after all dispersions, reflections, restrictions by apertures and any other losses. It is not the light flux which was sent to the sample in case Transmittance calculation.

If you measure reflectance and transmission together then probably original light flux can be measured as well then let denote it as I_o. In this terms T = I_t / (I_o - R)

Thanks @Andrei Pipa ..I will go through it and let you know if the problem is solved.

You can measure the thickness by coating on a quartz material then you can hope for expected results as glass may give you error even after calibrations by optical thickness meter

%R + %T + %A = 100% (R= reflection, T= transmission, A= absorption)

extinction (E) = -lg(1/T)

Raw Reflectànce is converted to absorbance using the function ,Absorbance=-log(10)*Reflectànce, commonly referred to as log (1/R).

Absorptance is from 0 to 1, it should not be confused with absorbance (from Wikipedia)

There are two main values that can be used to generally describe the absorption within a material. One is absorbance, and the other is absorptance.

Absorbance is defined as the logarithmic ratio of the intensity of the light incident on your sample (I0) to the intensity of the light passing through your sample (I). In chemistry, typically log10 is used, whereas in other fields (biology, etc.), typically ln is used. The equation is:

A = log10(I0/I) =  -log10(I/I0) = -log10(T)

where T is the fractional transmittance through the sample.

Absorptance is defined as the fraction of incident electromagnetic power absorbed by the material. It can be calculated from the simple RATS equation:

R + A + T + S = 1

where R is the reflectance, A is the absorptance (not to be confused with the "A" used for absorbance, which typically uses the same symbol), T is the transmittance, and S is the scattering from the material. All of these values are fractional.

Thus, if you are reading an absolute value of the "absorptance" from the Perkin-Elmer (with values of ~1.2 or 4.5), you are likely reading the absorbance. To obtain the fractional value, the true absorptance, you can apply the following equation:

%A = 100% - %T - %R -%S

Most of the time, you can assume that %S is negligible, but to obtain a true value of the absorbance of your sample, you would need both %T and %R measurements.

Note that if you assume %R is also negligible, then if you calculate %A = 100% - %T, the value you obtain should be identical to the value you get if you convert the "A" obtained from the Perkin Elmer (let's call it APE) to absorptance:

%A = 100% - %T = (1 - 10-APE ) * 100%

Hope this helps!

Sources: Andor.com "Absorption / Transmission / Reflection Spectroscopy" and Wikipedia ("Absorptance" and "Absorbance").