UV254 / SAC / UVA


UV254 as a parameter refers to ultraviolet light at wavelength 254nm and is used as a water quality measurement. This works by producing a UV light passing through a sample, with known volume or pathlength, to an optical sensor which will determine how much light was transmitted through the sample and how much UV light was absorbed by impurities. Data produced from UV254 measurements have units in UV absorbance (Abs) and UV Transmittance (%). UV254 is used to give rapid results for water quality as it is instant measurement and can be used continuously to deliver trends and alert to changes in the water.

Our eyes can detect light from the visible light spectrum in the 380-700nm range. Below 380nm is the UV spectrum and this is where very small particles are detectable, so UV254 is great for measuring organics and micropollutants which are invisible to the human eye.

The UV254 parameter can be used for constant UVT monitoring, giving continuous, real time results or for spot-checking different points in a water course. UV254 can be used as a Spectral Absorbance Coefficient (SAC) measurement by taking the Abs unit. As well as a standalone measurement it can be used to produce surrogate parameters, UV254 can detect aromatic bonds, such as those found in lab sampling measurements Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and Total Organic Contents (TOC).

Using UV254 requires a sample as a point of reference, using distilled or deionised (DI) water as the calibration point allows the device to identify any impurities in samples. It can be correlated to BOD, COD and TOC using extrapolation and by taking reference samples


UV254 is measured using an analyser with a UV bulb and a sensor which determines the transmission and absorption. It can be measured using analysing probe or using UV254 Go! quartz glass cuvette-based sensor.

The probes come in a range of pathlengths tailored to client needs, the 2mm UV254 Probe is ideal for wastewater and the 10mm optical path is designed to measure drinking water sources. Other probes are available for every extreme including ultrapure water, highly contaminated effluent and all in between. The larger the pathlength the higher the accuracy of UV254 measurement. Our UV254 Go! Controller uses a similar method to the probe but uses variable sized cuvettes rather than probe pathlengths.

UV254 and SAC can also be measured using a table top photometer.

UV Light Lightbulb


Real time UV254 results are obtained using analysis probe or cuvette sensor and displayed on a controller. This data can be integrated with SCADA systems or transferred using IoT, GSM, memory card or logged directly on the controller.

UV254 data can be presented in trends to determine is there is a spike in pollution, if a storm event occurs or there has been a drop in the quality in water. The UV254 parameter produces data which can be used by water companies, for environmental or trade effluent monitoring.

The data obtained from measuring UV254 allows for instant water quality measuring at WTPs, WwTPs, CSOs, aeration control, industrial effluent as wells as integrity testing of UV disinfection systems.


Lisburn BT28 2GN, GB

About us

Photonic Measurements is:
Incorporated in N.Ireland (NI622996) 
VAT registered in UK (GB192976846)
VAT registered in N.Ireland (XI192976846000)

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