# What is the Difference Between Absorbance and Fluorescence

The key difference between absorbance and fluorescence is that we can use an absorbance analysis technique to directly measure the amount of a specific wavelength that is absorbed by a sample without dilution or assay preparation, whereas fluorescence analysis requires sample preparation in which sample of interest must be bound with the fluorescent reagents in an assay kit.

Absorbance and fluorescence are important analytical techniques that we can use to detect different properties in a given sample.

### CONTENTS

1. Overview and Key Difference
2. What is Absorbance
3. What is Fluorescence
4. Absorbance vs Fluorescence in Tabular Form
5. Summary – Absorbance vs Fluorescence

## What is Absorbance?

Absorbance is a measure of the capacity of a substance to absorb light of a specified wavelength. Specifically, it is equal to the logarithm of the reciprocal of the transmittance. Unlike optical density, absorbance measures the quantity of light absorbed by a substance.

Furthermore, spectroscopy measures absorbance (using colorimeter or spectrophotometer). The absorbance is a dimensionless property, unlike most other physical properties. There are two ways to explain absorbance: as the light absorbed by a sample or as the light transmitted through a sample. The equation for the calculation of absorbance is as follows:

A = log10(I0/I)

Where A is absorbance, I0 is the radiation transmitted from the sample, and I is the incident radiation. The following equation is also similar to the above equation in terms of transmittance (T).

A = -log10T

## What is Fluorescence?

Fluorescence is the emission of light from a substance that has absorbed energy previously. Such substances have to absorb light or any other electromagnetic radiation to emit light as fluorescence. Furthermore, this emitted light is a type of luminescence, meaning it emits spontaneously. The emitted light often has a longer wavelength than the absorbed light. That means the emitted light energy is lower than absorbed energy.

During the process of fluorescence, light is emitted as a result of the excitation of atoms in the substance. The absorbed energy is often released as luminescence in a very short time period, about 10-8 seconds. That means we can observe fluorescence as soon as we remove the source of radiation that causes excitation.

There are many applications of fluorescence in different fields, such as mineralogy, gemology, medicine, chemical sensors, biochemical research, dyes, biological detectors, fluorescent lamp production, etc. Moreover, we can find this process as a natural process as well; for example, in some minerals.

## What is the Difference Between Absorbance and Fluorescence?

Absorbance and fluorescence are important analytical techniques that we can use to detect different properties in a given sample. The key difference between absorbance and fluorescence is that we can use an absorbance analysis technique to directly measure the amount of a specific wavelength that is absorbed by a sample without dilution or assay preparation, whereas fluorescence analysis requires sample preparation in which sample of interest must be bound with the fluorescent reagents in an assay kit. Moreover, the fluorescence technique is more effective than absorbance because the assay in fluorescence is highly specific for the target analyte.

The below infographic presents the differences between absorbance and fluorescence in tabular form for side by side comparison

## Summary – Absorbance vs Fluorescence

Absorbance is a measure of the capacity of a substance to absorb light of a specified wavelength. Fluorescence is the emission of light from a substance that has absorbed energy previously. The key difference between absorbance and fluorescence is that we can use an absorbance analysis technique to directly measure the amount of a specific wavelength that is absorbed by a sample without dilution or assay preparation, whereas fluorescence analysis requires sample preparation in which sample of interest must be bound with the fluorescent reagents in an assay kit.