Can you compare low-pressure and medium-pressure UV lamps?

The use of low and medium-pressure UV lamps in disinfection systems is a common occurrence. But to get to the point where a company or utility decides on the best solution to employ for their needs there are plenty of considerations to work through – including the choice of using low (LP) or medium-pressure (MP) UV lamps.
Posted: Monday, 6 March 2023

Can you compare the two?

If you were to Google ‘which is better, low-pressure or medium-pressure UV lamps’ you will come across many viewpoints and graphs that claim to provide the answer – such as this one below.  

At first glance, it appears that low-pressure (LP) lamps easily outperform medium-pressure (MP) lamps when it comes to disinfection performance. These graphs, however, need to be looked at more closely as what you often find is that they show relative intensity outputs (this one is from 200-400nm). The relative intensity in the context of these graphs means the output at each wavelength is plotted as a percentage of the highest output that each individual lamp type can produce within the specified range.

These graphs essentially show two key pieces of information:

1. LP UV lamps are monochromatic and so produce a single wavelength of 254nm, while MP UV lamps are polychromatic and produce an array of wavelengths

2. LP UV lamps can be more efficient in their energy usage for disinfection systems

However, these graphs should not be confused with the true output of an individual lamp.

When it comes to the output capabilities of each lamp type, they are considerably different and need to be analysed using different sets of comparative parameters.  

How can you compare?

If you were to compare irradiance (the amount of light or other radiant energy striking a given area of a surface) based on the lamps running at average outputs for each type, then you will see a very different graph appearing.    

As MP lamps run at powers from 400-10,000W as opposed to LP lamps that generally run at below 320W, MP lamps can output approximately 10 times more energy than LP lamps with a useful range across the full UV spectrum.

This also means MP UV lamps can be run for shorter times to achieve similar results to LP lamps and be used in other industrial applications such as curing, bonding and coating.  

Do you really need to choose between the two lamps?

A broader comparison of the lamps’ features versus the specific requirements of a system will provide a better way of comparing between the two types. Some of the considerations can be seen in the table below:

Looking at each point in turn…

If you are to use the lamps in a water disinfection system, then LP lamps do not operate in temperatures below 5°C or above 40°C, so use in low or variable water temperatures can be problematic. Conversely, as MP lamps operate at 600-900°C they are much less affected by outside temperatures.

As MP lamps are more powerful, they put off more heat. Therefore, with MP lamps you will need a higher flow rate to keep the system cool but will need fewer and shorter lamps to treat the substance. This translates into needing less space for the operating system, which is very useful if space is at a premium such as on a boat or in a small building.

In contrast, LP UV lamps get longer in size as their wattage increases, so any higher-powered LP UV system needs more space. As they use less power to generate their single wavelength in the UV-C range, they can be more energy efficient and have a much longer lamp life.

It’s also worth noting that the control system of MP UV lamps can adjust the energy of the UV output while that of LP UV lamps cannot.  

So, it depends on your specific requirements

What this means is that both LP and MP lamps have their own pros and cons to using them. As mentioned in the opening paragraph the choice of lamps to use in a system has multiple considerations that are far beyond the simple choice of looking at any single output table or graph.

This can make either LP or MP lamps the correct choice depending on the specific circumstances when you take into consideration wider factors such as budget, location, the system they are to be used in and the outputs required.

If you have a question about using LP or MP UV lamps, please get in touch via the  page and our technical team would be happy to help answer it for you.   

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