Hot Cathode vs. Cold Cathode UV Bulb; Are Long Life, Easy Start UV Bulbs worth purchasing?
Long Life, Easy Start UV Bulbs; Are Cold Cathode, Low Output UV Lamps worth purchasing?
UV-C Bulb Problems
First a little background information:
UV-C Hot Cathode Quartz Germicidal Lights/Bulbs 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 bulb starter or electronic ballast 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 itself (not output).
Operation at low temperatures as found in many ponds in the Winter or early Spring may result in excessive lamp blackening and more rapid depreciation in ultraviolet output. As well, starting of the Hot Cathode lamps at low temperature may require a few minutes.
It is also noteworthy that the tungsten filament used in the High Output UV-C Hot Cathode Quartz Germicidal versus many cold cathode are more fragile and burn out more quickly, especially with many "starts".
Some high end Compact Hot Cathode Germicidal Lights/Bulbs such as those made by Norman Lamps UV; G23, G11 have small metal pre-heat elements that aid in starting and reduce cold start times and wear and tear on the filament.
Norman Lamp Resource: Norman Lamps Compact UV Bulbs
Because of the voltage surge required by a Hot Cathode UV-C Bulb to light, ANY electronic ballast that is not providing this voltage due to age, damage, or simply poor quality, WILL fail to light a new Hot Cathode while this same ballast can still light an older hot cathode or a new cold cathode.
Hot cathodes generally achieve much higher power density than cold cathodes lamps and therefore produce more energy per given watt of energy used, making these a more desirable type of UV Bulb/Lamp for this reason alone. Despite the shorter life, and requirement for optimum functioning ballast to light aside; these UV lamps produce an optimum UV-C at 254nm, which is what you need for proper sterilization!
NEXT, COLD CATHODE LAMPS:
Cold cathode lamps have no thermionic emission coating to wear out and can have much longer lives than hot cathode thermionic emission tubes, however cold cathode lamps are less efficient than Hot Cathode lamps lamps because the cathode fall voltage is much higher (See Resources). Many sellers of these lower price, longer life, cold cathode UV bulbs, claim these bulbs will provide longer life & easy/quick lamp starts often at a much lower price. Often these are sold at eBay and many "Top Bulb" sellers that come up on Google's new spammy algorithm.
While this is true, these lamps/bulbs produce UV-C irradiation that can be as low as 185nm (which produces undesirable ozone) and as high as 330nm (which is UVB, not UVC).
With as little as 7% desirable UVC with these cold cathode bulbs; How is saving a few dollars and getting a few extra months life worth a bulb that is almost useless compared to a vastly superior Hot Cathode full UVC Bulb????
Obviously I am providing generalizations since these lights can vary, but what is clear is you are not achieving the optimum UV-C at 254nm.
See:UV (UVC) Lamps/Bulbs used in Aquariums/Ponds and How they Work
For a graph that shows HOW LITTLE UVC ENERGY IS PRODUCED BY THESE COLD CATHODE UV BULBS THAT ARE NOW COMMONLY SOLD!
Sadly many buyers are impressed by the "easy starts" and "low price" that these cold cathode UV Bulbs provide and the fact that these long life/low output UV Bulbs will often light in UV Sterilizers with worn ballasts that do not have the energy (voltage surge) to fire/start a new Hot Cathode Germicidal UV-C lamp/bulb.
Add to this problem that many UV Sterilizer ballasts degrade quickly (especially when used for ponds where more moisture is present) resulting in the un-informed user believing that their low end UV bulb is actually better than a a premium UV-C Hot Cathode Quartz Germicidal Light/Bulb when the OPPOSITE is the truth!
Even popular UV Sterilizers such as the over rated Turbo Twist has a high ballast degradation rate.
See: Potential UV Sterilizer Problems; Weak or Poor Quality Ballasts.
Purchasing a High Output 254nm UV-C Hot Cathode Germicidal Bulb for a UV with a weak/degraded ballast that will not light/fire a high output bulb, then purchasing a low output long life bulb that does work with this weak ballast is not an indicator of bulb quality, rather a lack of understanding of what makes a TRUE UVC producing lamp!!!
UV Bulb Resource: High Output Germicidal Bulbs
Unfortunately many manufacturers now even sell these almost useless for UVC sterilization cold cathode UV bulbs. As these will almost always light, and this allows for UV Sterilizers with a poor ballast designs that do not last long to appear to be functioning.
Worse yet, I have had customers/clients forward emails/letter claiming only their "original equipment" UV replacement bulbs should be used as their UV Sterilizers may not light the vastly superior hot cathode UV Bulbs.
The result, if a potential customer falls for this incorrect line of reasoning, is a UV Sterilizer that is almost a useless device as it is producing a fraction of the necessary UVC energy for level one or two sterilization or even clarification!
This is putting the blame in the wrong place, keeping a UV Sterilizer with a ballast that has degraded and then only using cold cathode UV Bulbs makes no sense at all; why have a UV Sterilizer that is only 7-15% effective??
Such is the case with this sarcastic email:
"If many manufacturers are using easy start bulbs to make up for so called "weak ballasts" then why does the website (selling hot cathode UVC Bulbs) say hot cathode bulbs are compatible with their units? They clearly are not compatible with the majority of units."
The logic here totally escapes me!!
- First this is not true, I am speaking about degraded ballasts, as even a new Coralife will fire a hot cathode "True" UV-C bulb, but a degraded electronic ballast will not.
Using the Coralife again as an example, my aquarium maintenance business has serviced many of these over the last decade, with a high quality UV C lamp working fine, but once the ballast degrades, only a cold cathode or 'old' (mostly expired) hot cathode will fire (it is noteworthy that the life span of a Coralife ballast is lower than many UVs). The FACTS are that these ARE compatible with the majority of unit, assuming a fully functional, non degraded electronic ballast/transformer.
- Second; Such a comment shows a total lack of understanding of fluorescent ballasts.
A magnetic ballast would not have such a problem, since these utilize a fluorescent starter to provide correct "surge" voltage to light the UV-C Bulb.
However most UV Sterilizers/Clarifiers utilize electronic ballasts of which many have poor circuitry that is easily degraded, especially by moisture; Once this happens a hot cathode true UVC Bulb cannot light.
See: Weak of Poor Quality Ballasts
- Third; the UV-C bulbs I have used and sold in my professional endeavors of aquarium/pond design and maintenance do and have worked in the majority of units
- Forth; (and I will repeat myself), why would you want a UV Sterilizer that only makes a "pretty blue light" that is about 7-15% effective for UV Sterilization??
See also: Electronic UV Sterilizer Ballasts; Lamp Problems
The bottom line is do not be fooled either by the low price, long life claims, or ease of lighting (or lighting at all with a weak ballast) of these long life/easy start UV Bulbs, as these are not the reason you should be purchasing a replacement UV Bulb.
Your UV Sterilizer is meant for Sterilization (not a pretty "blue" light) and this will NOT be achieved with these low output UV bulbs (especially level 2 sterilization)!!
Unfortunately some manufactures utilize low output UV bulbs such as Hagen Laguna; these UV bulbs are very inferior to high output UV bulbs and the result is no Level One UV Sterilization and even poor Green Water control.
For further resources see these articles:
*UV Sterilization; Facts & Myths
*UV Bulb Troubleshooting Guide
For the Best Very Best UV Sterilizer for your Pond or Aquarium:
TMC Advantage & Vecton Premium UV Sterilizer
There is not any better UV Sterilizer for both durability and UV-C irradiation effectiveness than the TMC Advantage and Vecton UV Sterilizer line, at any price!