Absorption spectroscopy: Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation due to its interaction with a sample, as a function of wavelength. Absorption spectroscopy is useful in chemical analysis because of its specificity and its quantitative nature. The specificity of absorption spectra allows compounds to be distinguished from one another in a mixture. An absorption spectrum can be quantitatively related to the amount of material present using the Beer-Lambert law.

Absorption spectrum: Illustrates the wavelengths absorbed by an individual microbe. 

Action spectrum: Illustrates the wavelengths that are most effective for disinfection.

AlN: Aluminium nitride (AlN) is a nitride of aluminum. Its wurtzite phase (w-AlN) is a wide band gap (6.2 eV) semiconductor material, giving it potential application for deep ultraviolet optoelectronics.

Beer Lambert Law: The Beer-Lambert law (Beer’s law) relates the absorption of light to the properties of the material through which the light is traveling; the absorbance varies linearly with the distance the light travels through the absorbing material (i.e., the path length) and the concentration of the absorber.

Disinfection: 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: 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.

Fluorescence: Fluorescence is the emission of light by a substance that has absorbed light. In most cases, the emitted light has a longer wavelength than the absorbed radiation.

Fluorescence spectroscopy: Fluorescence spectroscopy analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites molecules of certain compounds and causes them to emit light. Devices that measure fluorescence are called fluorometers. Many analytical procedures in chemistry involve the use of a fluorometer, usually with a single exciting wavelength and single detection wavelength. Because of the sensitivity that the method affords, fluorescent molecule concentrations as low as 1 part per trillion can be measured. 

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

LED: A light-emitting diode (LED) is a semiconductor light source. High brightness LEDs are available across wavelengths from ultraviolet to infrared. 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. LEDs present many advantages over traditional light sources such as lamps including lower energy consumption, improved safety, smaller footprint, and faster switching. 

Log reduction: Log reduction 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.

MOCVD: Metal organic chemical vapor deposition (MOCVD) is a chemical vapor deposition method for growing crystalline layers to create complex semiconductor multilayer structures. The growth of crystals is by chemical reaction and has become a major process in the manufacture of optoelectronic devices such as LEDs and lasers.

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

Radiant intensity: Radiant intensity is defined as the optical power emitted per unit solid angle. The SI unit of radiant intensity is watts per steradian (W·sr−1).

Spectrophotometry: Spectrophotometry is a method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution. The basic principle is that each compound absorbs or transmits light over a certain range of wavelengths. This measurement can also be used to measure the amount of a known chemical substance.

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.