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Absorbance to Transmittance Calculator

Absorbance Formula: A = -log10(T) = 2 - log10(%T)

Example: An absorbance reading of 1.00 corresponds to exactly 10.0% transmittance (90% light absorbed).

Interactive Converter

Beer-Lambert Law Context

Absorbance (A) is directly proportional to solute concentration in a solution. Most laboratory spectrophotometers read absorbance values between 0.1 and 1.5 with maximum accuracy. Above 2.0, the light transmitted is less than 1%, causing high detection errors.

A = 0: 100% T (no absorption)
A = 0.301: 50% T (half-light absorbed)
A = 1.0: 10% T (90% absorbed)
A = 2.0: 1% T (99% absorbed)

Absorbance to %T Benchmarks

Absorbance (A) Transmittance (%T) Optical Significance
0.00 100% Perfect transmission, no absorption
0.10 79.4% Typical light organic solvent baseline
0.50 31.6% Standard protein concentration reading
1.00 10.0% High concentration, 90% of light absorbed
2.00 1.0% Very dark solution, 99% of light absorbed
3.00 0.1% Near limit of standard spectrophotometer

Absorbance vs Transmittance

Transmittance (%T) measures the percentage of light that passes through a sample unabsorbed. Absorbance (A) measures the fraction of light absorbed. They are logarithmically related — absorbance increases linearly with concentration, while transmittance decreases exponentially.

A = −log₁₀(T) where T = decimal transmittance
%T = 10^(−A) × 100
Linear relationship: A ∝ concentration
Nonlinear: %T ∝ 1/concentration

Spectrophotometry Best Practices

Cuvette handling: Always handle cuvettes by frosted sides only. Wipe clear faces with lint-free tissue. Ensure no bubbles or scratches on optical path. Blank calibration: Use a blank (solvent only) to zero the instrument before each measurement series.

Wavelength selection: Set the instrument to λ_max (wavelength of maximum absorption) for highest sensitivity. For nucleic acids, use 260 nm; for proteins, 280 nm; for Bradford assay, 595 nm. Avoid the UV range (<340 nm) for routine work — visible range cuvettes absorb UV.

Frequently Asked Questions — Spectrophotometry

What is the formula to convert absorbance to transmittance?
Transmittance (%T) = 10^(-A) × 100, where A is absorbance. Alternatively, %T = 10^(2−A) when using the log10 form. Example: A = 0.5 → %T = 10^(-0.5) × 100 = 31.6%.
What is the Beer-Lambert Law?
The Beer-Lambert Law states A = εlc, where A is absorbance, ε is molar absorptivity (L/mol·cm), l is path length (cm), and c is concentration (mol/L). It explains why absorbance is directly proportional to concentration — the basis for spectrophotometric analysis.
What absorbance reading range is most accurate?
Most spectrophotometers achieve maximum accuracy between 0.1 and 1.5 absorbance units (approximately 80% to 3% transmittance). Below 0.1 A, stray light causes errors. Above 1.5 A, very little light reaches the detector, increasing noise. Dilute concentrated samples to bring readings into range.
What does an absorbance of 1.0 mean?
An absorbance of 1.0 means exactly 90% of incident light is absorbed by the sample, and only 10% is transmitted. A = 1.0 ↔ %T = 10.0%. This is a common benchmark — solutions with A = 1.0 contain the standard concentration for many colorimetric assays.
How do you convert absorbance to concentration?
Using Beer-Lambert Law: c = A / (ε × l). If you have a calibration curve (A vs. known concentrations), plot absorbance on y-axis and concentration on x-axis, then interpolate. Most lab software performs linear regression: A = m × c + b, then c = (A − b) / m.

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