The paper “Standardization of Methods for Fluence (UV Dose) Determination in Bench-Scale UV Experiments” by James R. Bolton and Karl G. Linden (2003) presents a basic standard procedure for determining UV fluence (UV dose) in laboratory experiments. The aim of the paper is to standardize experimental methods for UV disinfection and to ensure the comparability of scientific results in water treatment.
Ultraviolet light has established itself as an efficient method for inactivating pathogenic microorganisms in drinking water and wastewater.

The mechanism is based on the absorption of UV radiation by nucleic acids, which leads to dimerization of pyrimidine bases and thus prevents the replication of DNA or RNA. Wavelengths around 254 nm, as emitted by low-pressure mercury lamps, are particularly effective.
There are major differences in the literature regarding the design, calibration, and implementation of UV experiments. Among other things, the type of lamp, distance to the sample, homogeneity of the radiation, and calculation of the dose varied. This variability made it difficult to compare dose-response curves and led to uncertainties in regulatory applications and the technical implementation of UV disinfection systems.
Bolton and Linden developed a uniform methodology for determining fluence that is applicable to both monochromatic (low-pressure) and polychromatic (medium-pressure) UV light sources (BSM-03CBD) and proposes an irradiation chamber. The aim of the irradiation chamber is to achieve homogeneous, quasi-parallel irradiation of the water surface in order to ensure uniform fluence distribution.

The protocol includes:

• the mechanical construction of the irradiation chamber,
• the calibration of the measuring instruments,
• the mathematical correction of the radiation parameters,
• as well as guidelines for microbiological and safety aspects

Description of the standard protocol:

The fluence is defined as the product of the fluence rate (E) and the irradiation time (t):
The measurement is performed with a radiometer whose sensor is positioned at the height of the water surface. To increase the measurement accuracy, several correction factors are taken into account:

• Reflection factor: loss due to reflection at the water surface (~2.5%)
• Petri factor: correction for inhomogeneity across the sample area (should be > 0.9)
• Water factor: consideration of UV absorption in water according to Beer–Lambert‘s law
• Divergence factor: Correction for the non-completely parallel beam path

For medium-pressure lamps, the sensor factor (spectral sensitivity of the detector) and the germicidal factor (weighting of the wavelengths) are also taken into account.
 

Microbiological test procedure
 

• Stirring: Homogeneous mixing of the suspension without vortex formation.
• Irradiation with different dose values
• Replicates: At least three repetitions per dose value; perform dose-response curves at least twice.
• Randomization: Random order of irradiation to minimize systematic errors.
• Evaluation: Calculation of the log10 reduction of microorganisms as a function of dose and linear regression to determine UV sensitivity.
   

The paper defines a complete, internationally recognized protocol for standardizing UV disinfection tests on a laboratory scale.
Through precise correction methods, defined design requirements, and microbiological guidelines, it provides the basis for reproducible and comparable results in determining UV fluence-effect relationships.
The Bolton & Linden (2003) method remains the reference standard for laboratory testing with collimated beam systems and is central to regulatory applications such as DIN 19294, validation testing, and the development of industrial UV disinfection technologies.