Written by J.A Dobado | Last Updated on April 22, 2024

What is actinometry?

Light is a fundamental and ubiquitous form of energy in our world, and it plays a crucial role in many scientific fields, including chemistry, physics, and biology. However, measuring the intensity of light and its impact on chemical reactions can be challenging. This is where actinometry comes in..

Actinometry is a technique used to measure the intensity of light by monitoring the rate of a chemical reaction that is directly or indirectly affected by light. This allows us to quantify the energy of light and understand its impact on various chemical processes..

History of actinometry

The history of actinometry dates back to the 19th century when scientists were first exploring the properties of light. It was during this time that scientists discovered the phenomenon of photochemistry – the ability of light to induce chemical reactions..

In the early 1900s, actinometry became a useful tool in the field of photochemistry. It allowed researchers to determine the amount of light required to induce a specific photochemical reaction accurately. The concept of actinometry quickly spread to other fields such as atmospheric chemistry, environmental science, and materials science..

How actinometry works

Actinometry works by measuring the rate of a chemical reaction that is affected by light. In photochemical reactions, light is absorbed by a molecule, which results in the molecule’s excitation to a higher energy state. This excitation may cause the molecule to undergo a chemical reaction or initiate a chain reaction, leading to the formation of reactive intermediates..

To perform an actinometric measurement, a chemical reaction that is affected by light is selected. The reaction’s rate is then measured under controlled lighting conditions, and the light intensity is calculated using the reaction’s rate equation..

Examples of chemical actinometry

The measurement of radiant flux through the yield of a chemical reaction is known as chemical actinometry. This technique relies on a chemical that has a well-established quantum yield and produces reaction products that can be easily analyzed.

Potassium ferrioxalate is a widely used actinometer due to its simplicity and sensitivity across a range of relevant wavelengths. However, some actinometers, such as malachite green leucocyanides and vanadium(V)–iron(III) oxalate, undergo dark reactions, which can cause undesirable corrections.

Organic actinometers, such as butyrophenone and piperylene, are analyzed using gas chromatography. Reinecke’s salt is specific to the near-UV region, but is thermally unstable. Uranyl oxalate is toxic and challenging to analyze. Newer investigations have explored the use of radical scavengers, such as 2-nitrobenzaldehyde and benzoic acid, for nitrate photolysis measurements.

Meso-diphenylhelianthrene is useful for chemical actinometry in the visible range, specifically in the 475–610 nm range, but can be used for wider spectral ranges if the light source’s emission spectrum is known.

The photochemical reduction of mercuric chloride to calomel by oxalates is known as the Eder reaction. It has been demonstrated to be a highly efficient chain reaction with a chain length approaching 1000000, and it is frequently employed in various forms of actinometry, such as x-ray actinometry.

Applications of actinometry

Actinometry has numerous applications in various fields, including:

  1. Photovoltaics: Actinometry is used to determine the efficiency of solar cells by measuring the amount of light that is absorbed and converted into electrical energy..
  2. Environmental Science: Actinometry is used to determine the intensity of UV radiation in the atmosphere and its impact on the environment..
  3. Materials Science: Actinometry is used to study the properties of materials that are sensitive to light, such as photochromic materials..


Actinometry is a useful technique in various fields of science and technology. It provides a quantitative measurement of light intensity and allows for the optimization of processes that require light as an energy source. By selecting appropriate actinometers and experimental conditions, researchers can accurately determine the radiant flux of different light sources and optimize their experimental designs accordingly. The development of new actinometers and improvement in existing ones continues to enhance the accuracy and versatility of this technique, making it an essential tool in many fields..