Low or Medium-Pressure UV Lamps – Which is better for water disinfection?

There are two different types of UV lamps that are most commonly used to help purify water in disinfection systems, low-pressure lamps and medium-pressure lamps. So, what are the pros and cons of each, and which is better for water disinfection?
Posted: Tuesday, 18 September 2018

Low-pressure lamps are physically longer with a lower output per lamp of under 1000W. Low-pressure lamps only emit a monochromatic wavelength of 185 nm or 253.4 nm at high intensity. Medium-pressure lamps are considerably shorter with a high output of 200-50,000W and a wide wavelength between 200-600nm at various intensities. 


Low-pressure (254nm) lamps have an effective wavelength for disrupting a microorganism’s DNA, resulting in it being unable to replicate. However, a medium-pressure (200-600nm) UV lamp achieves a substantially better disinfection result at the same UV dose level. This is because although a low-pressure UV lamp will disrupt the microorganism’s DNA, at that wavelength it is possible for the DNA to be repaired, meaning the microorganism can repair themselves and continue to replicate and grow.

In contrast, a medium-pressure lamp severely damages the DNA which makes it far harder, and therefore less likely, that it will be able to be repaired. For example, the Cryptosporidium and Bacillus subtilis spores are inactivated most efficiently at 270-271nm which is beyond the low-pressure lamp’s capability, but well within the capability of a medium-pressure lamp. 

Power Efficiency

It is well known that low-pressure lamps tend to be more power efficient. However, to combat this, medium-pressure systems use an amplification mechanism that compensates for this by making the whole power consumption for a UV system the same as a low-pressure lamp. 


Due to the efficiency of medium-pressure lamps, the UV systems require fewer physical lamps than the lower-pressure ones. Having fewer lamps makes it easier to control each lamp individually, lowers the initial outlay cost of the system and means that fewer replacement and spare lamps will be required.

Overall, each lamp has their advantages and disadvantages that need to be considered when choosing the right lamp. However, when looking at the criteria above, medium-pressure lamps have a substantial advantage over the low-pressure lamps.

If you would like to know more about the comparisons of lamps or to find out what medium and low-pressure lamps Alpha-Purify can provide please get in touch. Contact Us.

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