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Absorption vs. Absorbance: What's the Difference?

By Aimie Carlson & Janet White || Updated on March 4, 2024
Absorption refers to the process by which a substance takes in another substance, whereas absorbance measures the amount of light absorbed by a solution.

Key Differences

Absorption involves a material, such as a gas or liquid, incorporating particles from another substance, often leading to a physical or chemical change. This process can occur through various mechanisms, including diffusion, osmosis, or chemical reactions, depending on the nature of the substances involved. On the other hand, absorbance is a specific term used primarily in spectroscopy to quantify how much light a sample absorbs at a particular wavelength. It is a dimensionless unit, calculated from the intensity of light before and after it passes through the sample, providing insight into the sample's properties.
While absorption can occur with various forms of energy or matter, including sound, light, or fluids, absorbance specifically deals with the absorption of light. Absorption in materials can lead to changes in their physical state or energy levels, such as warming up, dissolving, or undergoing a chemical transformation. Whereas, absorbance is used to analyze the concentration of solutes in solution, the presence of specific compounds, or the purity of a sample, making it a crucial parameter in fields like chemistry, biology, and environmental science.
Absorption is a broad concept that applies to multiple disciplines, from physics and chemistry to biology and environmental science, illustrating a fundamental property of matter and energy. It explains how substances interact with and incorporate various forms of energy or other materials. Conversely, absorbance is a more specialized concept that plays a vital role in analytical techniques, such as UV-Vis spectroscopy, enabling scientists to study molecular structures, chemical concentrations, and reaction kinetics with precision.
The efficiency of absorption processes varies widely depending on the materials involved and the conditions under which they interact, such as temperature, pressure, and concentration gradients. These factors can significantly influence the rate and extent of absorption, affecting everything from industrial processes to natural phenomena. In contrast, absorbance values are influenced by factors such as the concentration of absorbing molecules in the sample, the path length of the light through the material, and the specific wavelength of light, requiring careful control of experimental conditions to obtain accurate measurements.
In everyday contexts, absorption is observed in phenomena like sponge soaking up water or skin absorbing lotion, demonstrating its relevance to a wide range of practical applications and natural processes. Absorbance, while not a common everyday term, is essential in scientific research and industrial applications where precise measurement of light absorption by materials is necessary for quality control, diagnostics, and analytical purposes.

Comparison Chart


The process of taking in or soaking up substances
A measure of the amount of light absorbed by a sample


Broad, including physics, chemistry, biology
Mostly in spectroscopy and analytical chemistry


Varies (e.g., m^2/kg, dB)
Dimensionless (logarithmic scale)

Influencing Factors

Material properties, temperature, concentration
Concentration, path length, wavelength of light

Field of Study

General across many sciences
Specific to optical analysis

Absorption and Absorbance Definitions


Process by which one substance incorporates another.
A sponge absorbs water when it is dipped into it.


Measurement indicating how much light a substance absorbs.
Higher absorbance indicates more light absorbed by the solution.


In biology, the uptake of nutrients or drugs by living organisms.
The small intestine absorbs nutrients from digested food.


Relies on Beer-Lambert Law for quantitative analysis.
Absorbance is directly proportional to the concentration of the absorbing species.


In materials science, the penetration of a liquid into a solid by capillary action.
Paper towels absorb spills through capillary action.


Used in UV-Vis spectroscopy to determine concentration.
Absorbance measurements can identify unknown substance concentrations.


In physics, the conversion of sound or light energy into heat.
Dark surfaces absorb more sunlight than light surfaces.


Dimensionless, calculated from the intensity of light.
Absorbance is calculated by comparing the intensity of incoming and transmitted light.


In chemistry, the dissolution of a gas into a liquid or solid.
Carbon dioxide is absorbed by water in the ocean.


Essential for studying molecular interactions.
Absorbance spectroscopy can reveal details about molecular binding events.


The act or process of absorbing or the condition of being absorbed.


(physics) A logarithmic measure of the amount of light that is absorbed when passing through a substance; the capacity of a substance to absorb light of a given wavelength; optical density.


A state of mental concentration.


The act or process of absorbing or of being absorbed as,


(obsolete) engulfing; swallowing up, as of bodies or land.


Assimilation; incorporation.
The absorption of a smaller tribe into a larger
The absorption of bodies in a whirlpool


The imbibing or reception by molecular or chemical action, of radiant energy; the process of being neutrons being absorbed by the nucleus; interception.
The absorption of light, heat, electricity, etc.


(meteorology) The process in which incident radiant energy is retained by a substance (such as an air mass) by conversion to some other form of energy (such as heat).


(physiology) in living organisms, the process by which the materials of growth and nutrition are absorbed and conveyed to the tissues and organs; taking in by various means, such as by osmosis.


Entire engrossment or occupation of the mind.
Absorption in some employment


Mental assimilation.


(electrical engineering) The retaining of electrical energy for a short time after it has been introduced to the dielectric.


The act or process of absorbing or sucking in anything, or of being absorbed and made to disappear; as, the absorption of bodies in a whirlpool, the absorption of a smaller tribe into a larger.


An imbibing or reception by molecular or chemical action; as, the absorption of light, heat, electricity, etc.


In living organisms, the process by which the materials of growth and nutrition are absorbed and conveyed to the tissues and organs.


Entire engrossment or occupation of the mind; as, absorption in some employment.


(chemistry) a process in which one substance permeates another; a fluid permeates or is dissolved by a liquid or solid


(physics) the process in which incident radiated energy is retained without reflection or transmission on passing through a medium;
The absorption of photons by atoms or molecules


The social process of absorbing one cultural group into harmony with another


The process of absorbing nutrients into the body after digestion


Complete attention; intense mental effort


The mental state of being preoccupied by something


What is absorption?

Absorption is the process through which one substance captures or incorporates another, which can occur in various forms, including energy (like light or heat) or matter (such as liquids or gases).

What is the significance of absorbance in chemistry?

Absorbance is crucial in chemistry for determining the concentration of solutes in a solution, analyzing the purity of compounds, and studying reaction kinetics.

Can absorption apply to energy?

Yes, absorption can apply to different forms of energy, including light and sound, where the energy is converted into another form, typically heat.

What is absorbance?

Absorbance is a measurement that indicates how much light is absorbed by a substance, often used in spectroscopy for analytical purposes.

How do absorption and absorbance differ?

Absorption is a broad term referring to a physical or chemical process, whereas absorbance specifically measures the extent to which a substance absorbs light.

How do materials' properties affect absorption?

The properties of materials, such as their porosity, chemical composition, and physical structure, significantly affect their absorption capabilities.

Can absorption be reversed?

Depending on the context, absorption can be reversible, such as in physical absorption processes, or irreversible, as in chemical absorption.

What is the Beer-Lambert law?

The Beer-Lambert law is a principle in spectroscopy that relates the absorbance of light by a material to its concentration and the path length of light through the material.

Is absorbance a direct measure of concentration?

Absorbance can be used as a direct measure of concentration, following the Beer-Lambert law, which establishes a linear relationship between absorbance and concentration under specific conditions.

What is the importance of the path length in absorbance measurements?

The path length is crucial in absorbance measurements because the Beer-Lambert law states that absorbance is directly proportional to the path length of light through the absorbing medium.

What factors affect absorbance readings?

Absorbance readings are affected by the concentration of the absorbing material, the path length of light through the sample, and the wavelength of the incident light.

What is an example of absorption in daily life?

A common example of absorption in daily life is a sponge absorbing water, showcasing how materials can incorporate liquids into their structure.

Can absorbance be used to identify substances?

Yes, absorbance can be used to identify substances by analyzing their absorbance spectra, which are unique patterns of light absorption at different wavelengths.

How is absorbance measured?

Absorbance is measured using spectrophotometers, which quantify the amount of light absorbed by a sample at specific wavelengths.

What factors influence absorption?

Factors influencing absorption include the nature of the absorbing and absorbed substances, their concentration, and environmental conditions like temperature and pressure.

In what fields is absorbance commonly used?

Absorbance is commonly used in fields such as analytical chemistry, biochemistry, and environmental science for measuring the concentration of substances and analyzing chemical reactions.

How does wavelength affect absorbance?

The wavelength of light affects absorbance because different substances absorb light more strongly at specific wavelengths, which can be used to identify and quantify them.

How does temperature affect absorption?

Temperature can significantly affect absorption, as it may change the solubility of gases in liquids or the rate of chemical reactions, affecting the absorption process.

Why is absorbance considered dimensionless?

Absorbance is considered dimensionless because it is a ratio of the intensity of incoming light to the intensity of transmitted light, independent of unit.

What is a practical application of absorbance in healthcare?

A practical application of absorbance in healthcare is in diagnosing diseases, where it is used to measure the concentrations of specific biomolecules in blood samples, aiding in disease detection and monitoring.
About Author
Written by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.
Co-written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.

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