The Need to Change the UV Lamp

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Posted on September 23, 2015
Ultraviolet (UV) water treatment systems can seem a bit of a mystery, but are, in fact, really quiteUV light easy to understand.  A UV system works by passing UV light, light of a special wavelength (UV-C), through the water, and those rays are absorbed by any microorganisms present in the water.  As a result, their DNA is altered, and they cannot reproduce or create infection.  Through this simple process, UV light rays effectively inactivate E.coli, Giardia, Cryptosporidium and a whole bunch of other microbes- but these some of the more common illness-causing ones that can get into your drinking water.

The Need to Change Your UV Lamp

The key to UV disinfection is that different amounts of UV-C energy are needed to inactivate different bugs or organisms. The
amount of energy needed is called the dose.
UV doseAnd yes, it’s like a dose of medication in that you have to determine how much is needed to be effective. For UV systems, you get the dose by multiplying the light intensity by the exposure time.
The exposure time is accounted for by the flow rate of the water through the UV chamber; while the light intensity is primarily accounted for by the design and quality of the lamp.  But to spare you all the math, manufacturers of UV systems will typically design the system to provide a dose of 30 m J/cm2. This is sufficient to inactivate the microorganisms commonly found in water supplies (see table).

Select Microbes

That dose is typically guaranteed for about 9000 hours, or around one year of non-stop operation.    After that, the lamp needs to be replaced. Why?  Because the UVC intensity degrades over time, much the same way that the potency of a medication diminishes over time. Continuing to use your UV lamp beyond the prescribed 9000 hours is like taking medication after its expiry date. Just because it’s in your medicine chest doesn’t mean it will protect your health. Just because the UV lamp is still lit doesn’t mean it will protect you, either.

Many UV systems are equipped with a countdown timer or other visual cue or even an audible alarm to alert you to the need to change the lamp. Your water treatment professional may even provide an annual service to keep you on track. VIQUA also provides a lamp reminder service.


It’s important to note that at the end of the year, the lamp is likely to still be shining, 9000 hrsbut the UV intensity won’t be sufficient.  So regardless of how you remember to get it done, changing the lamp once a year is critical to ensure proper disinfection of your water supply.