The Ultimate List of UVC LED Disinfection Terms and Definitions

James Peterson

By Klaran

Below are a list of common terms and their definitions used in the specification of deep ultraviolet (UVC) LEDs for disinfection and application requirements for these devices.

Absorption Spectrum

Illustrates the wavelengths absorbed by an individual microbe. 

Action Spectrum

Illustrates the wavelengths that are most effective for disinfection.

B Value

The percentage of the LED population operating outside specifications. This value is used to represent the reliability of a population of LEDs at specific operating conditions. 


Disinfection is the process that removes, deactivates or kills pathogens (disease-causing microorganisms). Water disinfection can be achieved by physical or chemical means. Chemical disinfection is when a chemical agent (i.e. chlorine, iodine, ozone) must be added to the water for disinfection and the water undergoes chemical changes. Physical disinfection is a physical means of inactivating or removing bacteria (i.e. boiling, filtration, UV light).


Dose (or fluence) is the amount of UV radiation to which a surface is exposed and is measured in millijoule seconds per cm2 (mJ/cm2). UV dose is the product of UV irradiance and exposure time.


Far UVC refers to UV light in the 207 nm to 222 nm range. 

Germicidal UVC Range

UVC light emitted in the 250 nm to 280 nm wavelength range is typically referred to as the germicidal UVC range. This is because most pathogens have a peak UVC absorption in this range.

Indicator Organism

Micro-organisms whose presence indicates the probable presence of other harmful pathogens in a system or on a surface. 


Irradiance is defined as the optical power (radiant flux) per unit area incident on a surface.


A light-emitting diode (LED) is a semiconductor device which emits light when an electric current passes through it. When a light-emitting diode is forward-biased (switched on), electrons from the n-side recombine with holes from the p-side at the p-n junction resulting in the emission of light. The wavelength of the emitted light is determined by the energy gap of the semiconductor.

Log Reduction

Log reduction, also known as Log Reduction Value (LRV) is a way to denote levels of decreased biological contamination in water by factors of 10. A 1-log reduction is equivalent to a 90 percent reduction. A 2-log reduction would be 99 percent reduction and a 3-log reduction would be 99.9 percent reduction. A 99.99 percent reduction would be called a 4-log reduction.

Low Level Disinfection (LLD)

Low level disinfection is the disinfection of non-critical items, such as stethoscopes and blood pressure cuffs, that come in to contact with skin. 

L Value

The percentage of LED power output at comparing with the initial power output. This value is used to represent lifetime of an LED under specific operating conditions and application requirements. 

Optical Power 

Optical power (or radiant flux) is the total energy emitted by a light source across all wavelengths, measured in watts.

Point-of-Use (POU) Water Purification 

A point-of-use (POU) water purification system is installed at an individual point in a home or building, such as a faucet.

Point-of-Entry (POE) Water Purification 

A point-of-entry (POE) water purification system is installed to treat water upon entry into a house or building.

Spectral Sensitivity

Spectral sensitivity is the relative response to light (or instance, absorption) as a function of wavelength. Wavelengths that stimulate a maximum response characterize the peak spectral sensitivity. This is a dimensionless quantity, and typically normalized to a reference wavelength.

Surrogate Organism

Micro-organisms that behave similar to target microbes but are more practical for microbiological testing of disinfection systems because they are safer or easier to control in a laboratory environment. 

Target Microbe

Pathogen who is the primary target of disinfection in a specific application or specified by a regulatory standard. 


Deep ultraviolet, or UVC, refers to light with wavelengths between 200 to 280 nanometers (nm). It is used for inactivating the DNA of pathogens in many disinfection applications. 

Ultraviolet Transmittance (UVT)

UV transmittance (UVT) is a measurement of the amount of ultraviolet light that passes a given distance through a water sample. UVT can greatly impact the UV dose required in a system as particles in the water that absorb UV light will reduce the disinfection dose delivered to pathogens in the water. Typical UVT measurements are taken at a transmittance of 254 nm wavelength due to the prevalence of low-pressure mercury lamps in traditional systems. 

Viewing Angle

Viewing angle is the full angle at which the radiant intensity is half of the direct, on-axis intensity.

Wall Plug Efficiency

Wall plug efficiency refers to the effectiveness of the LED in converting the input electrical power to light output. It is defined as the ratio of the output optical power to the input electrical power.

Water Disinfection

The application of sufficient UV energy to flowing water in order to perform disinfection at a stated reduction rate of an organism.

Water Maintenance

The application of UV energy to standing water or wet surfaces inside of a water system to control microbe growth.