How Do You Calculate Total Absorption of a Sample from Its Absorbance Spectrum?

[Rositta]

Hi, does anyone know how to calculate the total absorptin of a sample from its labdam-absorbance spectrum?
I found a paper where the author find it as the average of the data, another one numerically integrate the spectrum over the whole lambda range.. but the two methods give different results... what's the corecct way?

 

[mfb]

Average of what data?

An integration over the wavelength spectrum, with the spectral intensity of the light source as weight, should give the correst result.