How UV Lamps, Bulbs Work; Low/Medium Pressure, Coatings

 

Updated 1/2/19

UV (UVC) Lamps (Bulbs) used in Aquariums and Ponds and how they work.

Recommended further reading:
Actual UV-C Emission from a UV Bulb; Aquarium or Pond

This post is primarily dealing with UV bulbs(or lamps), that emit UVC radiation.
These UV lamps to be referenced here are used in the Aquarium/Pond Industry. I will discuss other UV bulb types as well, since these may someday show up in the Aquarium/pond Industry.

There are two common UVC emitting lamps types currently employed for pond or aquarium UV Sterilization: the low pressure and the medium pressure mercury lamp.
http://www.uvreplacmentbulbs.com

*The low pressure lamp emits its radiant energy between 250-260 NM which is where UV Sterilization is most effective with a UVC efficiency of about 38- 95%.
The emission peak of the Mercury electron transition within these low pressure (hot cathode) UV lamps is fixed in both energy and wavelength.

*The medium pressure lamp emits its radiant energy between 250 and 350 with many energy spikes in between (most notably around 320 which is more in the UVB range) with a UVC efficiency around 7-15%.

CAUTION: Many Medium-Pressure UV bulb/lamp manufacturers incorrectly boast that the broad UV spectral output of these lamps is more effective, which in reality is the exact opposite!!



The low pressure lamp used by most all Premium Aquarium & Pond UV Sterilizers (not always the low end UVs such as Jebo & AquaTop) is clearly the better choice based on this information.
The low pressure lamp does have one flaw which the medium pressure lamp does not suffer from and that is the low pressure lamp is affected by water (or air) temperatures and operates best between 20 C (68 F) and 40 C (104 F).
Generally this is not a major concern considering most aquarists operate their aquariums well within this range. With ponds, this is still not a major concern in that most problems, including algae occur in warmer months. This problem can be also addressed with in-line heaters to pre-warm the water.

Many UV Sterilizers come with quartz sleeves which form an air pocket between the lamps and water that in theory increases operating temperatures.
HOWEVER my own tests have shown this improvement to be nominal at best especially when compared to a well designed direct contact UV Sterilizer.
In a test with a custom 15 Watt UV Sterilizer and a 13 Watt Quartz sleeve UV Sterilizer (a well designed one at that), the increase in temperate was only 2 degrees F (I have observed up to 5 degrees depending on the units compared).
This test started at 68 F and was conducted over 15 minutes, then water was removed from the units and the temperature measured. Unfortunately the quartz sleeve is accepted as a standard that sounds great in theory, but in practicality is not a significant improvement in most applications (I would recommend them in some applications such as Lobster tanks, but even here a pre-heater would also be recommended).

Please see references for which sterilizers used in this test:
Custom 15 Watt UV Sterilizer
13 Watt Quartz sleeve UV Sterilizer

Please see this article for much more about UV Sterilization:
ULTRAVIOLET STERILIZATION (How UV sterilization works)
This article explains the benefits and myths about aquarium and pond uv sterilization


Chemical Coating in UV Lamps/Bulbs

A few companies now provide a coating that they claim extend lamp output and lamp life. I have serious doubts to these claims based on the fact the emission peak of the Mercury electron transition is fixed in both energy and wavelength and I don't think coatings can emit additional UV to any advantage. Coatings usually capture UV and convert the emission wavelength via further energy transitions to some visible part of the spectrum, perhaps with several spectral peaks depending upon the composition of the coating.

One such company, Emperor Aquatics, makes the claim that their UV Lamps feature an internal chemical coating that provides added resistance to solarization.
This company uses a picture of a new bulb/lamp with the coating and a one without. HOWEVER I in my 30 + years have never witnessed the degradation shown in this picture, and I suspect that Emperor Aquatics is using an Ozone producing UV bulb/lamp to make their point.
I stand by my experience that these coatings are simply a gimmick to charge more for their proprietary UV Bulbs

UV Lamps/Bulbs Starting

Another aspect of UV lamps that should be noted is how they function or start. Most quality UV lamps commonly used are Hot Cathode (low pressure) UV lamps. The Hot Cathode Germicidal UV Lamps are similar in their operation to the standard fluorescent lamps.
The Hot Cathode lamp operates from a ballast or transformer and requires a device such as the glow switch starter to preheat the electrodes in order to start the lamp. The electrodes, located at the ends of the lamp, are tungsten filaments coated with emission material and, under normal operation, govern the life of the lamp. In view of the fact that the life of the electrodes is shortened by frequent starts, the lamp life is rated according to the number of times the lamp is started.

Operation at low temperatures may result in excessive lamp blackening and rapid depreciation in ultraviolet 'C' output.

See Also this related post:
Long Life, Easy Start UV Bulbs

References:
*Aquarium/Pond UV Sterilizer Use
*UV Lamps & UVC Lamp Types
*UV-C Bulb Specifications; Aquarium and Pond

Pond UV Truths; Sterilizer, Clarifiers

 

Pond UV Sterilizers vs. Aquarium UV Sterilizers; is there a difference?

Updated 7/29/13

The answer is yes AND no.
This said I have had persons over the years tell me that a store (or web site) stated that a UV sterilizer that is made for a pond is even better for an aquarium; the truth is this is generally false, however for clarification, please read on!



Here is what one might look for in a Pond UV Sterilizer:

*Heavy duty construction so as to withstand the sun light and other elements.
However any UV that is even indirectly protected form the elements (sun light, heavy rain or snow) will work fine for a pond, assuming otherwise good construction.

*Pre filtration of debris;
This is probably the most important aspect of a pond UV Sterilizer in that most ponds have higher amounts of organics in the water as well as general debris that will both clog a UV Sterilizer and significantly block UV effectiveness.

However even most of the UV Sterilizers specifically designed for ponds have no more ability to carry out this function than other UV Sterilizers.
This function must be added by way of a pre-filter or standard pond filter by which the water passes through before the UV Sterilizer.
See these resources: Hydro Pond Sponge Pre-Filters, Pressurized Pond Filters, & Submersible Pond Filters

It should be noted that some pond UV Sterilizers come with bulb/sleeve “wipers”, but these gimmicks do not keep the quartz sleeve much cleaner than simply one without. These wipers fail to remove hard water deposits well, which is the most common problem of UVC light blocking build-up on quartz sleeves.

Some claim that a quartz sleeve is necessary for pond UV sterilizers, this is only true for very cold ponds in which algae is not generally a problem anyway (this is not to say a Quartz sleeve is bad either as I have used many such as the Terminator or Premium TMC Pond Advantage UV Sterilizers that have quartz sleeves with good results). See these product resources: Premium TMC Pond Advantage & Vecton UV Sterilizers & SunSun Terminator Value UV Sterilizers

In truth, units with direct contact of water (such as the Custom 15 Watt UV Sterilizer or some Aquanetics models) actually clear many ponds in the summer just as effectively and are less fragile.

As an example, had a customer go through two Tetra UV Sterilizers until trying out the "custom UV" that I built, which performed much better (he lives in the warm summer climate of the Central Valley of California).
I should note that the design of my custom UV is similar to the TMC Advantage/Vecton line of Premium UV Sterilizers, minus the quartz sleeve.

Lets now look at what is really needed for both aquariums AND ponds for a UV to be effective:
*For algae control an average UV Sterilizer (some need slower flow rates due to poor design) require a flow rate of 40 -60 gph PER watt.
The compact UVs generally require a slower flow rate of 40-45 while the straight tube UVs can have higher flow rates of 45-60, with the TMC Advantage & Vecton UV Clarifier working well at flow rates of 60 gph per watt (or even higher) due to the exceptional flow design (dwell time).

* For bacterial control (Level One Sterilization) an average UV Sterilizer needs a flow rate of 20-30 gph PER watt (some need slower flow rates due to poor design, while others such as the TMC can get by with the higher flows of 35 watts per gph).
Reference: UV Sterilization; Level 1

* For Redox control an average UV Sterilizer (some need slower flow rates due to poor design) needs a flow rate of 25-30 gph PER watt

* For parasite control an average UV Sterilizer (some need slower flow rates due to poor design) needs a flow rate of 8-12 gph PER watt (generally almost ALL UV Sterilizers work to control parasites more by indirect means such as improved water conditions such as Redox and lower suspended bacterial counts).

Now lets look at the claims of the Tetra Pond UV Sterilizer:
9 Watt UV
• Maximum water flow:
900 gallons per hour
• Maximum pond size:
1800 gallons

5 Watt UV
• Maximum water flow:
330 gallons per hour
• Maximum pond size:
660 gallons

How do they get a jump of almost triple flow for less than double wattage increase?
Second the flow rate claims for both are outrageous for both algae and bacterial control. 900 gph calculates out to 100 gph per watt which is ridiculous, so someone who purchases this for a pond or aquarium thinking this will do a better job due to high flow rate claims are sadly mistaken.

The bottom line is do not buy a UV Sterilizer such as the one listed above for your aquarium or pond under the mistaken belief that it can handle more since it is called a pond UV. This is neither true for aquariums nor ponds.
This is also not to say that the above pond UV Sterilizer does not work, however it should not be purchased based on its claim of flow or simply because it is a "Pond" UV Sterilizer as that makes little difference in real world application.

If you are truly interested in high end UV Sterilizer for your aquarium that is primarily designed for ponds, consider a Pond UV Sterilizer with a high output (HO) UVC Bulb and longer exposure time based on a longer bulb (or quartz sleeve) and water contact via a UV with a design that utilizes this aspect of design.
See: High Output Straight Tube UVC Bulbs

A good example would be the TMC Pond Advantage 15, 25, 30, & 110 Watt UV Sterilizers or the Aqua HO UV Sterilizers (although the Aqua units generally cost much more with no more dwell/contact time as compared to the TMC units).
See: TMC Pond Advantage UV Sterilizers

In fact for larger ponds, you will not find a better UV Sterilizer/Clarifier in design, flow rate, durability, ease of obtaining replacement parts (which is where even many of the better UV Sterilizers fail), & over all effectiveness than the TMC line of UVs, which have long been recognized as a leader in Europe.
The picture above shows a breakdown of the TMC 110 Watt UV Sterilizer, Clarifier which is without equal for larger ponds (or even central aquarium systems), especially when price is considered.
See: TMC 110 Watt UV Sterilizer/Clarifier

For more about this subject please read this article about UV Sterilization:
Aquarium and Pond UV Sterilization; how it works, truths and myths

For other top quality UV product resources:
*UV Replacement Bulbs
*UV Sterilizer for Aquarium or Pond