The absorption measurement is given by A=-log(%T). In order to convert the values for absorption into transmission you will need to undo the log function.  A quick way to do this in Excel would be to create a new column that way you do not lose the original absorption data in your spread sheet.  If you absorption data is in column B and begins on row 2, then in cell C2 you should be able to convert by typing in the following formula =(10^(-B2))*100 this would give you the %T.  You can then click on the lower right hand corner of the cell and drag down and the formula will automatically update the cell address of the data point, this avoids having to repeatedly type the formula into Excel.  

I hope this helps 

The absorption measurement is given by A=-log(%T). In order to convert the values for absorption into transmission you will need to undo the log function.  A quick way to do this in Excel would be to create a new column that way you do not lose the original absorption data in your spread sheet.  If you absorption data is in column B and begins on row 2, then in cell C2 you should be able to convert by typing in the following formula =(10^(-B2))*100 this would give you the %T.  You can then click on the lower right hand corner of the cell and drag down and the formula will automatically update the cell address of the data point, this avoids having to repeatedly type the formula into Excel.  

I hope this helps 

Since A=-log(%T), you will need to undo the log function.  To accomplish this, if your absorption data begins in cell B2, you can type the following formula into cell C2, =(10^-B2)*100 this will convert the absorption measurement into percent transmission and will also preserve the original absorption data.  To avoid re-typing the formula for every cell, you can highlight cell C2, and then click the lower right corner of the cell, drag down to the end of your data and Excel should automatically update the formula. This should give you the complete transmission spectrum. I hope this helps.

It is not always advisable to convert transmission data to absorption data as reflection may also be effective. Unless you neglect it, you can't convert transmission data to absorption data or vice versa. Take care before doing that.

Yes, as Dr A. Kumar says. Scattering plays a role as well here, so if you have for example nanoparticles bigger than 10 nm diameter, they will scatter. That is why you need to be carefull about converting absorption into transmission.

Use this calculator:  http://www.epolin.com/converting-absorbance-transmittance 

Yes the formula and procedure told by Mr. Albert Dukes is really helpful. I too have tried this.

Are this equation is applicable for FTIR too?

T = 10(2-A)

A = 2 - log(T)

 http://www.epolin.com/converting-absorbance-transmittance

this will help you directly convert abosirbance into transmittance or vice-versa

You can use this formula:

A (Arb.units) =  2 - log10T(%)

if you have the lights transmittance data/ absorption data, do you have an excel file to then calculate the VT single value?

In general, a spectrophotometer working in the solar radiation wavelength region measures either the transmittance or the reflectance of a sample. That is, the absorbance is not measured directly, but is calculated from the measured transmittance and reflectance (if both can be measured). When a spectrophotometer gives you the absorbance A’ on the logarithmic form, i.e. the optical density OD, which is a common output from many spectrophotometers (OD = A’ = log10(1/T) = alog10(e)x = a’x, "10" supposed to be as a subscript here, i.e. the 10-log, where T is the transmittance, x is the penetration length or depth x, and a and a’ denote the absorption coefficients depending what form is used, which is deduced from the Beer-Lambert law), it is in reality a calculation from the measured transmittance ignoring the reflectance. A spectrophotometer measures the radiation which is collected by the detector from either the transmitted or the reflected beam. Furthermore: T + A + R = 1 (100 %) where T = transmittance, A = absorbance and R = reflectance between 0 to 1 (or between 0 to 100 %). Note that the absorbance A in the above is not the absorbance A’ on the logarithmic form, i.e. not the optical density OD, which is a common output from many spectrophotometers. You may see further details in e.g. chapter 3, 4, 7.6.3 and 7.6.7 in the following article: B. P. Jelle, ”Solar Radiation Glazing Factors for Window Panes, Glass Structures and Electrochromic Windows in Buildings - Measurement and Calculation”, Solar Energy Materials and Solar Cells, 116, 291-323, 2013. In addition, you need to have control over if the transmittance and reflectance are specular (directly transmitted or reflected, i.e. mirror-like) or diffuse (scattered in all directions), where you in the latter case would use integrating sphere accessories to collect the scattered transmitted/reflected radiation.

A = -log(%T/100)

You can follow this link also https://facultystaff.richmond.edu/~cstevens/301/excel1.html

Thank you Rajan

Absorbance (A)= (2)-(Log(%T) in excel

transmittance= Power(10,(2- Absorbance) in excel

transmittance= Power(10;(2- Absorbance) in open office spread sheet

As the absorption of electromagnetic radiation, e.g. also including ultraviolet (UV), visible (VIS), near infrared (NIR) and infrared (IR) radiation, follows the Beer-Lambert law, i.e. the radiation is decreasing exponentially with the penetration depth in the actual material, it is often helpful to plot the spectra on a logarithmic absorbance scale versus wavelength or wave number. Hence, a representative spectrum is chosen from each of the samples and plotted on a logarithmic absorbance scale for quantitative studies. Mathematically and physically it follows that a doubling of the logarithmic absorbance, also called optical density, is interpreted as a doubling of material thickness or a doubling of concentration of absorption active agents. In general, a spectrometer measures either the transmittance or the reflectance of a sample, i.e. measuring the radiation which is collected by the detector from either the transmitted or the reflected beam.

Furthermore:

T + A + R = 1 (100 %)

where T = transmittance, A = absorbance and R = reflectance between 0 to 1 (or between 0 to 100 %).

That is, the absorbance is not measured directly, but is calculated from the measured transmittance and reflectance (if both can be measured). When a spectrometer gives you the absorbance A’ on the logarithmic form, i.e. the optical density OD which is a common output from many spectrophotometers, it is in reality a calculation from the measured transmittance ignoring the reflectance.

The mathematical relationships are shown in the following (note that the common (Briggs) logarithm is denoted lg = log10 and the natural logarithm is denoted ln = loge, the latter one not directly used below):

The optical density OD is defined as the absorbance A' written on a logarithmic form by

OD = A’ = log10(1/T) = alog10(e)x = a’x

which is deduced from the Beer-Lambert law given by

I = I0e-ax

where the transmittance T is given by

T = I/I0

where the transmitted radiation intensity I decreases exponentially with the penetration length or depth x, I0 is the incident radiation intensity, and a and a' denote absorption coefficients depending what form is used.

In addition, you need to have control over if the transmittance and reflectance are specular (directly transmitted or reflected, i.e. mirror-like) or diffuse (scattered in all directions), where you in the latter case would use integrating sphere accessories to collect the scattered transmitted/reflected radiation.

For further information see e.g. chapter 3, 4, 7.6.3 and 7.6.7 in the following article (may be requested through ResearchGate): B. P. Jelle, ”Solar Radiation Glazing Factors for Window Panes, Glass Structures and Electrochromic Windows in Buildings - Measurement and Calculation”, Solar Energy Materials and Solar Cells, 116, 291-323, 2013.

In addition, the following articles may also be of interest: (a) B. P. Jelle, A. Gustavsen, T.-N. Nilsen and T. Jacobsen, ”Solar Material Protection Factor (SMPF) and Solar Skin Protection Factor (SSPF) for Window Panes and other Glass Structures in Buildings”, Solar Energy Materials and Solar Cells, 91, 342-354, 2007, (b) B. P. Jelle, T.-N. Nilsen, P. J. Hovde and A. Gustavsen, ”Accelerated Climate Aging of Building Materials and their Characterization by Fourier Transform Infrared Radiation Analysis”, Journal of Building Physics, 36, 99-112, 2012, and (c) B. P. Jelle and T.-N. Nilsen, ”Comparison of Accelerated Climate Ageing Methods of Polymer Building Materials by Attenuated Total Reflectance Fourier Transform Infrared Radiation Spectroscopy”, Construction and Building Materials, 25, 2122-2132, 2011.

by using this relation A = -log(%T/100)

Optical density or absorbance = 2 - log (%T), apply this formula for conversion or you can use following link

https://www.epolin.com/converting-absorbance-transmittance

Of the Beer-Lambert law -Log10(I/I0) = eps*c*d both sides of the equation are generally incorrect:

Right side:

Article Beer's Law – Why Absorbance Depends (Almost) Linearly on Concentration

Left side:

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Article The Electric Field Standing Wave Effect in Infrared Transmis...

Article The electric field standing wave effect in infrared transfle...

Oh!! Great !!! This is very benign question for newcomer.

However, If anyone desire to get, can follow this formula;

To convert a value from percent transmittance (%T) to absorbance, use the following equation:

• Absorbance = 2 – log(%T)
• Example: convert 56%T to absorbance:
• 2 – log(56) = 0.252 absorbance units

To convert a value from absorbance to percent transmittance, use the following equation:

• %T = antilog (2 – absorbance)
• Example: convert an absorbance of 0.505 to %T:
• antilog (2 – 0.505) = 31.3 %