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In light of ongoing battle against COVID-19, there has been considerable interest in the power of ultraviolet light (UV) for the disinfection of surfaces, particularly in the hospital environment. Although the efficacy against the spread of SARS-CoV-2 yet needs to be proven, the UV lighting technology shows a lot of promise.
The ultraviolet light (UV) is categorised into three different wavelength ranges: UVA (315-400nm), UVB (280-315nm), and UVC (100-280nm). The latter is often considered to be the “germicidal range” because the wavelengths between from 200nm and 300nm can disrupt nucleic acids of microorganisms and disrupt their DNA. This stops the replication process and inevitably results in the inactivation or death of organisms.
Currently known pathogens (a bacterium, virus, or other microorganisms that can cause disease) tend to have an associated absorption spectrum that shows how they respond to the UV light at specific wavelengths. This often referred to as the “germicidal effectiveness curve”.
Figure 1. Germicidal effectiveness curve for E.coli compared to UV-C LED emitting at 265nm (From Ultraviolet Germicidal Irradiation Handbook, Fig. 5.5)
How to design a UV disinfection system?
Several factors have to be considered when setting the specifications for the UV disinfection system.
- Target micro-organism
UV dose, or sometimes referred to as fluence, is an amount of UV radiation applied to the target disinfection area. This parameter is a function of radiation intensity (irradiance, mW/cm2) and exposure time (s), and generally expressed in mJ/cm2. The microorganisms that are being targeted tend to respond to UV light differently and require different levels of UV dosage. More complex microorganisms might need a higher dosage of UV light.
“Log reduction” is another important term to remember when it comes to measuring how effective the UV light is against the pathogens. The or is a mathematical expression that states the power to which the number 10 can be raised to achieve . For example etc. In microbiology, log reduction refers to a 10-fold or 90% reduction of bacteria and other pathogens. In other words, 1-log reduction means that there are 10 times or 90% fewer pathogens, 2-log reduction corresponds to 100 times or 99% reduction and the reduction continues by moving down the decimal place.
Once you identify what microorganisms you are targeting, the required dose and corresponding log reduction level can be selected. International Ultraviolet Association (IUVA) has the full list of dosage requirements for 4-log (99.99%) inactivation of various bacteria, protozoa, viruses, and algae, which is available on their website. However, keep in mind that these values for dosage were calculated for UV mercury lamp and therefore need to be adjusted for UV LED wavelengths.
- Target area
The other two parameters to consider are the area of a target surface as well as the distance from the UV light source to the surface. They both define the irradiance of the UV light, which is the power per unit area incident upon a surface at a specified distance. The irradiance is inversely proportional to the distance according to the inverse square law function. Commonly available software tools, including DIALux, can be used to model the irradiance distribution depending on the factors such as the surface area, a source-to-surface distance, as well as a quantity of UV LED sources and the distance between them.
Figure 2. UV LED source at h distance from a surface are of a x b
- Exposure time
From Eq. 1, it can be noticed that the required dose and irradiance level are linked through another important parameter called exposure time. Exposure time defines how long the UV light source needs to be active to achieve the target level of log reduction of the pathogens. The same dosage can be achieved by extending exposure time and lowering the irradiance level. This is particularly useful for low power applications, where the extended battery life is important. On the other hand, if there is a limited time available for disinfection, the higher power UV LEDs are required.
UV System components
The UV LED disinfection system generally consists of a single or a combination of UV LEDs, optical elements, and LED drivers. This article highlights electronic and optical devices that are necessary to build a complete UVC system.
The UV LEDs from Seoul Viosys are specifically designed for surface and water disinfection against pathogens, including E. coli and Staphylococcus aureus. They are available in three different packages: ceramic (AIN) CA3535 and AAP (metal frame) with a flat glass window and standard 3030 packages. The radiant flux of these LEDs ranges from a few mW for small consumer devices up to 60mW for high flux applications.
Technology |
3030 |
AAP 1-chip |
AAP 4-chip |
Part number |
CUD7QF1A |
CUD8AF1D |
CUD8AF4D |
RS Stock # |
|||
Peak λ |
275nm |
275nm |
275nm |
Radiant Flux (mW) |
1.6 |
19 |
60 |
If (mA) |
20 |
200 |
600 |
Vf (V) |
6 |
6.5 |
6.3 |
Beam angle |
125° |
120° |
118° |
The use of secondary optics is often necessary to ensure that the UV light from LEDs is focused on the target surface and uniform irradiation distribution is achieved. However, traditional LED lenses made from acrylic or polycarbonate materials are not suitable for UVC light. These materials tend to degrade upon being used under UVC irradiation. Furthermore, standard glass must be substituted by light quartz glass because the former is not transparent to UVC light.
Silicone and aluminium are widely utilized materials for UV optics. Silicone demonstrates a high transmission in UV wavelengths, including UVC range, and it is extremely suitable for complex optical lens designs. Meanwhile, pure aluminium is a highly reflective and cost-effective option for reflectors for UV.
UV optics from LEDiL, specifically, ZORYA, STELLA, and ALISE are suitable for UVC applications, and they are available for purchase through RS Components.
Figure 3. LEDiL lenses for UVC applications
Lastly, LED driver is required for functions such as powering the LEDs, regulating the flow of current, protecting from overvoltage and short circuit.
What tools can help to design the UV system?
Using Lighting System Selector mobile app from Future Lighting Solution (FLS) is an easy and interactive way to select LED light source and system components from your phone. Water and surface purification is just one of the potential applications for UV lighting along with air deodorization, horticulture, and skin treatment.
Figure 4. Lighting System Selector mobile app
Usable Light Tool is a web-based wizard that allows the users to evaluate the performance of high-power LEDs in the “real world” environment. The effect of critical factors on the light output such as forward current, forward voltage, dissipated power, and heat are considered.
Figure 5. Usable Light Tool v 2.4
Driver Selector Tool is an interactive tool that assists in selecting an optimal driver for LED light sources. All three FLS tools will require the users to create an account and an associated password to be able to access the content on them.
Figure 6. Driver Selector Tool
Are you involved in medical device design and manufacture?
Let us know in the comments section if you are involved in the response to the COVID-19 response in UVC disinfection system design.
Disclaimer: DesignSpark/RS Components/Seoul Viosys did not find scientific evidence to prove the efficacy of UVC LEDs against COVID-19.
Please follow this fact sheet from IUVA for their expert opinion.