UV-C Irradiance Requirements for Disinfection Applications and test method of UV-C lamp
Sep 24, 2024
UV-C Irradiance Requirements for Disinfection Applications
With the rapid growth of UV-C applications in germicidal and disinfection applications, there is a growing need to quantify and determine whether or not a particular UV-C lamp or setup will accomplish the disinfection objectives. Unlike regular lighting products that we can visually confirm if it's "bright enough," UV-C is invisible to the naked eye, and this can make it especially challenging from a measurement perspective. In this article, we will go over the primary measurement methods and principles, and then work through a few examples that will help work through the steps needed in determining the irradiance requirements for a particular setup.
1. What exactly is UV-C irradiance?
The trickiest, and perhaps most essential component in this equation is the irradiance value. Irradiance is the measure of how much energy falls on a particular surface. Irradiance can be influenced by three primary factors: (1) UV lamp strength, (2) distance from the lamp, and (3) angle relative to the lamp. It may be helpful to think about regular light bulbs behave - a very bright light bulb positioned far away and angled away from a surface, for example, will not provide sufficient illumination on a table surface.
2. Dosage = UV Amount + Time
When designing for UV-C disinfection, we need to start with UV-C dosage, because the ultimate goal is to achieve a certain UV-C dosage needed to inactivate the pathogen. But first, what exactly is dosage, and how is it measured?
UV-C dosage, also called exposure dosage or fluence, is a way to measure how much total UV-C energy has radiated a particular surface. This is the most crucial element in UV-C system design, because UV-C dosage is the primary determinant in whether or not we have successfully achieved pathogen inactivation.
Dosage is determined not only by the strength of the UV-C that falls on a surface, but also how long that surface is exposed to the UV-C radiation for. In other words, all else equal, a UV-C lamp with half the strength can achieve just as much UV-C dosage if it is used for twice the amount of time.
The strength of the UV-C that falls on a surface is called irradiance, and is measured in W/m² (or some variant of power per surface area). The exposure time is measured in seconds.
The simple form of the formula is shown below:
Exposure Dosage (J/m²) = UV Irradiance (W/m²) x Time (seconds)
We can also verify this by seeing that the units are in agreement here (1 Joule = 1 Watt-second).
3. Application-Specific Requirements
- Air Disinfection: Requires lower doses of UVC light, as air moves quickly and pathogens are dispersed.
- Surface Disinfection: Higher irradiance is required for surface disinfection, due to the need for deep penetration to neutralize microorganisms on various surfaces.
- Water Treatment: Water clarity affects the required UVC irradiance, with clearer water allowing lower irradiance levels, while turbid or colored water needs higher intensity to ensure all pathogens are reached.
Test method of UV lamp
UV-C Irradiance Measurement
The radiation intensity of the lamp: According to the formula of the ultraviolet radiation dose equal to the radiation intensity multiplied by the irradiation time, the extended irradiation time required for different intensities can be obtained, It can also be seen that the same sterilization effect can be obtained for a high intensity for a short time or a low intensity for a long time.
The number of lamps installed: According to national regulations, the number of indoor suspended ultraviolet disinfection lamps installed is an average of not less than 1.5W per cubic meter, and it is required to be evenly distributed and the height of the ceiling is 1.8-2.2m away from the ground to make people breathe. The belt is in the effective irradiation range.
Ambient temperature: Generally, room temperature 20-40 ℃ is the suitable temperature for ultraviolet disinfection. Within this temperature range, the intensity of ultraviolet radiation is the largest and stable, which can achieve the ideal disinfection effect.
Relative humidity: when the relative humidity is 55% -60%, ultraviolet rays have the strongest kill rate of microorganisms.
Strengthen the monitoring of the radiation intensity of the UV lamp tube: the UV lamp in use should be inspected once every 3-6 months with an ultraviolet radiation illuminance meter, and once a year with the ultraviolet radiation illuminance meter for measurement calibration to maintain accuracy. It can also be measured by the ultraviolet radiation intensity chemical indicator card. The indicator card is irradiated 1m away from the lamp tube for 1min. The photosensitive coating changes from white to purple red. Compared with the standard color block, the lamp radiation intensity can be known
Lamp Lifetime Testing
Another critical aspect of UV lamp testing is determining the operational lifespan, typically measured in hours of continuous operation before the UV-C output decreases below an effective level (usually 80% of initial irradiance). This test ensures that lamps will continue to provide effective disinfection throughout their rated lifespan.
- Procedure: Lamps are operated continuously or in simulated on-off cycles, and their UV-C output is periodically measured to track any decline in performance.
- Safety and Compliance Testing: UV lamps must also undergo safety tests to ensure they meet regulations for human exposure and operational safety. This includes testing for ozone generation, as some UV lamps produce harmful ozone as a by-product, which must be controlled or minimized.
- Procedure: Safety tests include measuring ozone levels, ensuring proper shielding to prevent harmful UV exposure, and testing the stability of the lamp in different operating conditions (temperature, humidity, etc.).
- Standards: Safety tests are governed by standards like IEC 62471 for UV radiation safety and UL 1598 for electrical safety compliance.
In summary, the success of UV-C disinfection depends on delivering the appropriate irradiance levels, which vary based on application requirements. Rigorous testing methods ensure that UV lamps meet performance, efficacy, and safety standards, guaranteeing their reliability in critical disinfection tasks.
