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Which UV Lamps are best suited for Aquatic Germicidal Disinfection?
Low-Pressure “Hard Quartz Glass” UV Lamps provide the greatest UV-C output from initial input watts, the longest useful lamp life, the greatest variety of styles and sizes, and are the most cost efficient.
The UV lamp is the most critical component of any UV Sterilizer. It determines the equipment size, initial purchase price, and cost of ownership. UV equipment is used with aquatic life support systems for the specific purposes of either germicidal disinfection or ozone destruction. When compared to any other UV lamp type (Medium-Pressure), the Low-Pressure “Hard Quartz Glass” UV lamp family delivers the highest UV-C Output of their initial Input Watts, offer the longest useful life, and generates the least amount of heat. They are the most “temperature compatible”, cost efficient, and offer the largest variety of sizes.
The following information is “third-party” validated. Here we demonstrate why Low-Pressure Hard Quartz Glass UV lamps are superior to Medium-Pressure or Low-Pressure/Low-Output Soft Glass UV Lamps (specifically for germicidal disinfection in aquatic life support systems).
Medium-Pressure UV Lamps vs. Low-Pressure UV Lamps
- Medium-Pressure Lamps produce 10 times more HEAT (1,600°F) than Low-Pressure Lamps (180°F max.).
- Medium-Pressure Lamps produce the majority of their UV Output in the UV-A and UV-B spectral areas (well outside the specific UV-C “Germicidal Spectrum”).
- Low-Pressure UV lamps produce 33-40% of their UV Output in the UV-C action spectrum, which is unmatched by Medium-Pressure Lamps (maximum 7-13%).
- Our high quality T5 Standard-Output, T5 HO and Amalgam UV lamps deliver an unmatched 9,000 hours of continual operation while retaining >80% efficiency, as opposed to Medium-Pressure Lamps’ typical life of between 700 to 4,000 hours while retaining as little as 60% efficiency.
- Low-Pressure Lamps’ “cost of ownership” is far LESS EXPENSIVE than Medium-Pressure Lamps, due to Medium-Pressure Lamps' short lamp life. Short lamp life requires that they be replaced much more frequently.
- In order to obtain the maximum life from a Medium-Pressure Lamp the lamp’s operating temperature must constantly be monitored and controlled. This increased level of control adds a higher level of sophistication & expense to the UV system.
Now that we have determined that Medium-Pressure UV Lamps are NOT suitable for Continuous-Flow Aquatic Life Support applications, we will focus our attention on the specific operating characteristics of four styles of Low-Pressure UV Lamps.
Operating Characteristics of the Four Styles of Low-Pressure UV Lamps
Each Low-Pressure UV Lamp style serves its own unique purpose based upon specific operating criteria and cost.
- Soft Glass Low-Output (LPLO): 25% to 33% UV-C Output/Maximum 8,000 hrs. useful life while retaining 60% efficiency.
- Coated, Hard Quartz Glass “Standard-Output” (LP): 33% to 40% UV-C Output/9,000 hrs. useful life while retaining >80% efficiency.
- Coated, Hard Quartz Glass “High-Output” (LPHO): 33% to 40% UV-C Output/9,000 hrs. useful life while retaining >80% efficiency.
- Coated, Hard Quartz Glass Amalgam lamps: 33% to 40% UV-C Output/9,000 hrs. useful life while retaining >80% efficiency.
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Medium-Pressure UV Lamp |
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1. Soft Glass UV Lamp |
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2. Standard-Output UV Lamp |
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3. High-Output UV Lamp |
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4. Amalgam UV Lamp |
Useful UV Lamp LifeLow-Pressure UV lamps are made of either soft-glass or hard-quartz glass. The difference between the two types of glass is that hard quartz glass is more resistant to solarization than inferior soft glass. Solarization is a by-product of UV lamp operation. During lamp operation, the mercury that is used to create the UV energy reacts with the applied electrical arc which, over time, forms a very gradual plating of mercury oxide onto the inside surface of the lamp’s glass envelope. This mercury oxide by-product reaction absorbs UV light, therefore reducing the UV-C light transmission through the lamp’s glass envelope.
End of Useful Lamp Life Comparison Soft Glass vs. Hard Quartz Glass UV Lamps
 NOTE: Click Chart for Larger view. UV-C OutputAll UV lamps convert a percentage of their “Input Watts” (the electrical power that drives them) into UV-C Output “Germicidal Watts”. UV-C light is the spectral (Germicidal Action Spectrum/240-280 nm) wavelength used to render “living microorganisms” incapable of reproducing. The comparison chart below demonstrates a significant contrast in UV-C output between Low-Pressure “Soft Glass” and “Hard Quartz Glass” UV Lamps. “Hard Quartz Glass” UV Lamps are preferred due to their exceptional input Watt to UV-C Output Watt conversion performance. At the beginning of this evaluation Medium-Pressure lamps were eliminated due to their poor UV-C output (7%-13% of initial input watts) but are still shown here for sake of comparison.
UV Lamp UV-C Output Comparison
 NOTE: Click Chart for Larger view. This UV-C Output Comparison chart shows that “Hard Quartz Glass” styles of Low-Pressure UV Lamps outperform Soft Glass Low-Pressure UV Lamps.
UV Lamp Operating TemperaturePractically all UV lamps in use today are affected by the temperature of their immediate environment! The temperature at which the lamp operates affects the UV-C output and can decrease it by as much as one percent per 1.5°F of temperature change from the lamp’s nominal operating temperature. Thermally protecting the lamp can be accomplished by using one of the two known methods. The first method is to sheath the lamp inside a transparent hard quartz glass sleeve. The quartz sleeve will isolate/insulate the lamp from the water by creating a protective temperature zone around the lamp. This is the preferred method.
The second method is to flow the water through a transparent quartz glass reactor with the lamp(s) positioned just outside and around the reactor. This method becomes considerably complex due to the sensitive control of air temperature around the lamp(s). In addition, the travel path of light photons is distorted due to the curvature of the quartz reactor. There is no creditable data supporting this method.
The “UV Lamp Operating Temperature Chart” below identifies the optimum lamp operating temperature as well as optimum application water temperature parameters for the various types of Low-Pressure UV Lamps.
UV Lamp Operating Temperature Comparison
 NOTE: Click Chart for Larger view. Note: The Medium-Pressure UV Lamp is not recommended for Aquatic Life Support applications due to its extreme operating temperature which causes a high incidence of quartz sleeve fouling and requires the use of complex sleeve wiper systems.
Soft Glass, Low-Pressure/Low-Output UV Lamps offer less UV-C Output, a shorter useful lamp life and a narrower Application Water Temperature Tolerance than the hard quartz glass UV Lamp styles and, therefore, have been eliminated from our evaluation. From this point forward we will focus only on the preferred Hard Quartz Glass Low-Pressure UV Lamps.
The Variations of “Hard Quartz Glass” Low-Pressure UV Lamps“Hard Quartz Glass” Low-Pressure UV Lamps are sub-divided into three categories: Standard-Output (LP), High-Output (LPHO), and Amalgam. Standard and High-Output lamps rely on mercury vapor, which emits UV light when excited by electricity. Amalgam lamps are different, they do not use liquid mercury but rather a mixture of bismuth, indium2 and mercury (amalgam) that is bound to the inside wall of the lamp’s glass envelope (amalgam spot).
Standard (LP) and High-Output (LPHO) UV Lamps’ mercury vapor pressure within their glass envelopes are governed by the temperature of tiny droplets of free flowing liquid mercury. The liquid mercury droplets collect at the coldest spot inside the lamp. Maximum UV-C output occurs when the mercury droplets are at a peak temperature of 107°F. The difference between Standard (LP) and High-Output (LPHO) lamps is that LPHO lamps are driven at a higher electrical current and input wattage, are equipped with heavier filaments, and are capable of carrying higher electrical loads. These “heavy duty” filaments also provide a more controlled cold spot (behind themselves) for mercury collection. This enables the lamp to produce greater levels of useable UV-C power (typically 2 times the power level of a Standard-Output UV Lamp).
Amalgam Lamps use a “fixed amalgam spot” in place of free flowing liquid mercury. This “amalgam spot” provides the optimum mercury vapor pressure at an operating temperature of 180° F. This allows for greater input current loads and, in turn, greater UV-C output. Additionally, the “amalgam spot” regulates the mercury during operation. If the internal lamp pressure falls, the “amalgam spot” releases mercury into the excited vapor. If the pressure rises, it will absorb mercury from the vapor. This inherent regulation maintains stable UV output while offering significantly broader water temperature tolerances (typically 2 times the power level of a High-Output UV Lamp).
UV Lamp Glass FormulationsThere are two “Hard Quartz Glass” formulations available: “VH” Glass (known as ozone producing) and “L” Glass (known as non-ozone producing). The “L” type glass formulation is preferred for germicidal applications because it does not produce ozone and, therefore, eliminates “lamp scaling”. “Lamp scaling” is a nitrogen residual by-product of a reaction between the ozone emitting lamp and the air (nitrogen) inside the quartz sleeve.
This nitrogen by-product coats the inside surfaces of the quartz sleeve and the exterior surface of the UV lamp. “Lamp scaling” is undesirable because it absorbs valuable UV-C light and, in turn, reduces the lamp’s output efficiency.
UV Lamp Glass Coatings
All Emperor Aquatics, Inc. Hard Quartz “L” Glass UV Lamps feature an internal chemical coating that provides added resistance to solarization. This chemical coating helps to stabilize the lamp’s energy deprecation over its useful life span and increase its efficiency from 60% (for an uncoated lamp) to > 80% (for a coated one). This additional performance coating does not decrease the UV-C output wattage of the lamp (See “G64T5L Lamp Depreciation Uncoated & Coated” chart below for details).
 NOTE: Click Chart for Larger view.
 UV Lamp Comparison ConclusionHard Quartz Glass, Low-Pressure UV Lamps: Unmatched Performance for Aquatic Life Support Applications!The preceding lamp performance information demonstrated that Medium-Pressure UV Lamps are not suitable for Continuous-Flow Aquatic Life Support applications. Additionally, we proved that Low-Pressure, Low-Output Soft-Glass UV lamps are inferior (in UV-C output and useful life) to the superior Hard Quartz Low-Pressure UV Lamps.
Now we will focus on which Hard Quartz Glass Low-Pressure UV lamp style is best suited for your Continuous-Flow Aquatic Life Support application.
- Low-Pressure Standard-Output (Hard Quartz Glass) UV Lampsare best suited for low flow applications not exceeding a flow rate of 350 GPM with a UV dose requirement of 30,000 µWs/cm². Benefits include: lower initial equipment cost and the least expensive replacement glass cost.
- Low-Pressure High-Output (Hard Quartz Glass) UV Lampsare best suited for moderate flow applications not exceeding 700 GPM with a UV dose requirement of 30,000 µWs/cm². Benefits include: Twice the UV-C output when compared to Standard-Output UV Lamps of the same dimensional size. HO lamps also require fewer lamps to achieve the same UV dose, and offer a broader water temperature tolerance.
- Low-Pressure Amalgam (Hard Quartz) UV Lampsare best suited for high flow applications (shell & tube models) of up to 3,380 GPM end of useful lamp at a UV dose of 30,000 µWs/cm². Benefits include: approximately twice the UV-C output when compared with High-Output UV Lamps and they require fewer lamps to achieve higher UV dosages.
If you still have questions regarding Ultraviolet Sterilization or UV Lamps please feel free to send us an e-mail here: Ultraviolet Lamp Questions.
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