A percentage transmission and an absorbance number describe the same defined power ratio on different scales.
Define the power ratio
Let P0 denote the reference radiant power and P the transmitted power under matching optical conditions. Decadic absorbance is A = log10(P0/P) = -log10(T), where T = P/P0. State the logarithm base when exchanging a result. A logarithm using base e produces a different numerical quantity. Primary reference: IUPAC: absorbance.
This ratio does not automatically isolate absorption from every loss in a practical measurement. The reference and treatment of cell walls, scattering and other contributions matter. Calling A an absorbed percentage loses both the logarithmic definition and the optical conditions.
Work through a fictional transmission pair
Consider an invented worksheet with reference power 100 units and sample power 25 units. T is 0.25, transmission is 25 percent and decadic A is about 0.60206. At sample power 50 units, T becomes 0.5 and A is about 0.30103. Doubling transmitted power halves A in this particular pair; it does not create a general linear scale.
The complement 1 - T is 0.75 for the first row. It is a fractional loss of the defined transmitted beam, not the number 0.60206. Keep separate columns so a reviewer cannot accidentally multiply absorbance by 100 and report an absorption percentage.
Build a ratio-to-log worksheet
Enter P0, P, T, percent transmission, log base and calculated A in separate fields. Recalculate one row directly from the raw powers rather than trusting a display label. Retain the reference identity with the wavelength and cell configuration.
For a second check, reconstruct T = 10^(-A) and compare it with the original ratio. A disagreement identifies an arithmetic or convention problem before anyone interprets sample composition. The invented powers demonstrate notation only and establish no product specification or laboratory acceptance limit.
Customer Questions
Is A = 0.60206 the same as 60.206 percent loss?
No; that row has T = 0.25.
Which logarithm is used here?
Base 10 is explicitly defined.
Does the example identify a chemical?
No; it only converts a ratio.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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