In spectrophotometry, the measurement of absorbance and transmittance are fundamental in analyzing the interactions between light and substances. These measurements are used extensively in chemical, pharmaceutical, and environmental testing to determine the concentration and identity of substances. A precise conversion between absorbance and transmittance is crucial for efficient data analysis. Alfa Chemistry provides the following calculators for converting absorbance and transmittance values to help improve the efficiency and accuracy of scientific measurements.
Absorbance to Transmittance Converter
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What is Absorbance?
Absorbance is a measure of the amount of light absorbed by a sample at a specific wavelength. It is a logarithmic function of transmittance, denoted by:
A=-log10(II0)
where:
- A is the absorbance,
- I0 is the intensity of the incident light,
- I is the intensity of the transmitted light.
Absorbance is dimensionless and typically measured in absorbance units (AU). High absorbance indicates that a sample absorbs a significant portion of the incident light.
What is Transmittance?
Transmittance, on the other hand, represents the fraction of light that passes through a substance. It is defined as the ratio of transmitted light (I) to incident light (I0):
T=II0
Transmittance is expressed as a percentage (%T), which is simply the ratio multiplied by 100:
%T=(II0)×100
Transmittance values range from 0% to 100%, where 100% indicates no absorption and 0% signifies complete absorption.
How is Absorbance Calculated from Transmittance?
The relationship between absorbance and transmittance is inversely logarithmic. The absorbance can be calculated using the following formula:
A=-log10(T)
A=2-log10(%T)
This formula highlights that as transmittance decreases, absorbance increases. This is because a higher proportion of light is absorbed by the sample when less light passes through it. This relationship is critical for converting transmittance data into absorbance, which is often more useful in spectrophotometric analysis.
Quick Reference in the Laboratory
A transmittance to absorbance table serves as a quick reference guide for converting transmittance values into
absorbance values without the need for complex calculations. Such tables are especially useful for rapid analysis in
the laboratory setting, where time is often of the essence.
Below is an example of a transmittance to absorbance table:
| Transmittance (%) | Absorbance (AU) |
| 100 | 0 |
| 99 | 0.004 |
| 98 | 0.009 |
| 95 | 0.022 |
| 90 | 0.046 |
| 85 | 0.071 |
| 80 | 0.097 |
| 75 | 0.125 |
| 70 | 0.155 |
| 65 | 0.187 |
| 60 | 0.222 |
| 50 | 0.301 |
| 45 | 0.347 |
| 40 | 0.398 |
| 35 | 0.456 |
| 30 | 0.523 |
| 20 | 0.699 |
| 10 | 1 |
| 5 | 1.301 |
| 1 | 2 |
This table provides a quick and convenient reference, eliminating the need for manual calculation and improving efficiency in both routine and advanced spectrophotometric analyses.
