The applications for UV disinfection continue to grow – moving from on-demand, low flow applications in point-of-use (POU) to more demanding point-of-entry residential water treatment. But designing UV disinfection systems can be challenging, especially when comparing existing solutions – UVC LEDs and low-pressure mercury lamps.
While these lamps provide specifications similar to other fluorescent lamps, it can be difficult to find the needed specs on light output in the UVC range, degradation, and other key information. UVC LEDs, on the other hand, are solid-state devices that can be tuned to meet specific application requirements. When comparing the two solutions, it’s important to understand how the power available for disinfection is calculated from the data sheet specifications–and ultimately how this is used in the application design.
Estimated Power Output
There are a wide range of mercury lamps on the market today. When searching for a UV lamp, the specified power is often the input wattage, not the output power for disinfection. Typical low pressure mercury lamps operate at about 30% wall plug efficiency with an emission at 254 nm. This, coupled with losses from lamp ballast and heat, a lamp’s actual output at 254 nm is 10 to 30 percent of the input rating. The higher percentage typically applies to better quality, larger, high power lamps. This means that when considering a 10 Watt lamp, a good assumption would be 1 Watt or 1000 mW are available for disinfection.
Now compare that to UVC LEDs.
A common myth around UVC LEDs is that you need the same UVC energy from the light source as lamps. In actuality, you can achieve the same level of performance with less UVC energy when designing with UVC LEDs because of both the peak wavelength and emission pattern.
If we were to compare a UVC LED to a UV lamp apples-to-apples in an application, one could assume that you would need thirteen 80 mW LEDs to reach the equivalent performance of the 10 W lamp. But that is not the complete picture because we still need to account for the difference in wavelength output. An advantage of LEDs is that they are available at peak wavelengths across the UVC range. For most microbes, 265 nm provides 20 to 30 percent better disinfection than 254 nm. With this information, ten 80 mW LEDs with peak output at 265 nm provide an equivalent disinfection power for the 10 W lamp.
The second important comparison between the two technologies has to do with the reactor design. Whereas lamp UVC output is across the entire length of the chamber, the LED provides a more uniform irradiance of the water as it passes across the light source. An LED is 8-10 times more intense at the point source than the apex of the lamp emission. Thus reactor designers can improve the disinfection performance of the reactor through reflective materials and flow design.
In POU, we’re talking about a very low flow rates where only modest amounts of LED power are needed to address it. In the past, more sophisticated reactor designs and materials might have been used to account for the lower LED power, but as we see higher power LEDs become more available, more basic designs and materials can be used. Many POU designers are achieving comparable performance to lamp designs with a handful of LEDs in their reactors as nominally there is a 10:1 benefit for LEDs over lamps in point-of-use (POU) applications. In the case of point-of-entry, which has higher flow rates, one can expect a 4:1 benefit over lamps.
Comprehensive Costs
If only equivalent intensity was the comparison, then it’s likely that UVC LEDs would have already replaced lamps in most disinfection applications. While pricing on UVC LEDs has dropped dramatically over the last few years, it is still important to use the strengths of LED design to build the most efficient systems. When designing a system, the overall product costs should be considered (rather than relying solely on lamp versus LED cost), even if that cost is comparable in some cases. The electronics of an LED can be smaller, simpler, cheaper, and more dependable than the ballast needed to power a lamp. In addition, with better control of a UVC LED emission pattern there is not always a need for expensive reflective material to make use of a lamp’s emitted UVC pattern.
Conclusion
LEDs provide more intense UVC energy in compact, robust packages and are already capable of replacing most UV lamps in small to medium-sized applications. Even as products get larger and more powerful, we at Crystal IS have application engineers with access to light extraction tools, calculators, and experience that can help determine how to integrate UVC LEDs into each product. If you’d like to learn more about using UVC LEDs for disinfection in your application, contact us today.