What is the Difference Between Absorbance and Transmittance?
🆚 Go to Comparative Table 🆚The main difference between absorbance and transmittance lies in the way they describe the interaction of light with a substance. Here are the key differences:
- Transmittance:
- Represents the fraction of incident light that is transmitted through the substance.
- Defined as T = I/Io, where I is the transmitted light and Io is the incident light.
- Can be expressed as a percentage (%T) by multiplying T by 100.
- Indicates the amount of light that passes through the sample.
- Absorbance:
- Represents the amount of light absorbed by the sample.
- Calculated from the transmittance (T) using the formula: Absorbance = 2 – log(%T).
- Also referred to as "optical density".
- Indicates how much of the light the sample absorbed.
Bothabsorbance and transmittance are measurements used in spectrophotometry, which is useful for determining the identity of an unknown substance and, with the use of a set of standards, determining a substance's concentration in a sample. While transmittance is a directly measurable quantity, absorbance must be calculated using the transmittance measurement.
Comparative Table: Absorbance vs Transmittance
Here is a table that highlights the differences between absorbance and transmittance:
Property | Transmittance | Absorbance |
---|---|---|
Definition | Transmittance is the fraction of incident light that is transmitted through a substance, defined as T = I/Io, where I = transmitted light and Io = incident light. | Absorbance is a measure of how much of the incident light is absorbed by a substance, calculated using the formula: A = log10(1/T) or A = 2 - log(%T). |
Range | Transmittance values range from 0 to 1. | Absorbance values can range from 0 upwards. |
Measurement | Transmittance measures how much light passes through a substance. | Absorbance measures how much of the incident light is absorbed by a substance. |
Increase with Path Length/Concentration | Transmittance decreases exponentially as the path length or concentration increases. | Absorbance increases linearly as the path length or concentration increases. |
Instrument | Spectrophotometers are used to measure transmittance. | Spectrophotometers are used to measure absorbance. |
In summary, transmittance is a measure of how much light passes through a substance, while absorbance is a measure of how much light is absorbed by a substance. These two properties are related through the Beer-Lambert law, which states that the absorbance of a solution is directly proportional to the path length of light through the material and the concentration of the absorbing substance.
- Absorptance vs Absorbance
- Optical Density vs Absorbance
- Absorbance vs Fluorescence
- Emission vs Absorption Spectra
- Absorption Spectrum vs Emission Spectrum
- Molar Absorptivity vs Specific Absorbance
- Absorptivity vs Molar Absorptivity
- Action Spectrum vs Absorption Spectrum
- Absorption vs Adsorption
- Calibration Curve Absorbance vs Concentration
- Atomic Absorption vs Atomic Emission
- Translucent vs Transparent
- Absorption vs Assimilation
- Atomic Absorption Spectroscopy vs UV Visible Spectroscopy
- Diffraction Grating vs Transmission Grating
- Excitation vs Absorption
- Digestion vs Absorption
- Colorimetry vs Spectrophotometry
- Diffraction vs Scattering