UV Light Transmittance TT134
Published on May 25, 2018

UV Light Transmittance - Tech Talk 134

UV transmittance (UVT) is not turbidity! The water’s clarity is not an effective indicator, because both solid and dissolved material can absorb UV light. For example: metals (iron) in water are not visible to the human eye but absorb UV light and have a negative impact on UVT.

UV Light Transmittance


UVT is the transmission of UV light (254 nm) through water. Regarding Aquaculture applications, flow-through fish-culture systems requiring influent disinfection typically test at 90-95%T. In contrast, RAS recirculating aquaculture systems typically test lower at 70-85%T. Application conditions vary and, therefore, must be evaluated individually.

 UVT must be considered when sizing any UV system. Using a meter is the only method of determining an application’s true %T. It is important to mention that UVT is not linear. The UVT Chart below reveals actual fluence (UV dose) loss based on % UV transmittance (%T).


The Real UVT Field Meter manufactured by RealTech Inc. is available in both in-line and portable versions. Your EAI Representative can assist you with more information.



UV Light Transmittance

The line-graph above illustrates how a lower %T parallels a diminished UV dose when operating our SafeGUARD UV System Model CLP960A8 at a flow-rate of 150 GPM. Notice the distinct drop in achieved UV dose with only a slight change in %T.