Light absorbance vs absorbance confusion?

Question

okay so on my paper i have unknown percentage light absorbance of 19, 20, and 23, and i have an equation of y=mx+b, where y is the absorbance and x is the concentration which i need to find by plugging in the absorbance for y. what confuses me is in the paper it said "20 light absorbance is 80% transmitted, percent absorbed does not equal absorbance" i am stuck because i have percentage of light absorbance of 19,20, and 23, am i suppose to subtract that from 100 and get result of that as my absorbance? but then wouldn't that be transmitted? 

Answer 1

No, you don't just subtract from 100.  The equation that relates absorbance to % transmittance is

A = 2 - log %T, so e.g. 10% transmittance = absorbance of 1 and 1 % transmittance = absorbance of 2.  In your examples, I'm assuming that you have %T not % A, as I've never heard of data obtained as %A, but %T is common.

If that's the case, then 19%T = 0.7212 Absorbance and 20%T = 0.699 Absorbance.  If, in fact, your data are actually % absorbance, then the % transmittance would be 100 - that number.  That would be very strange however.