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.