Since the discovery of UV germicidal efficacy in 1901, ultraviolet disinfection has mostly been carried out using low-pressure mercury lamps.
Mercury is present in low-pressure mercury lamps, which raises worries about contamination of the environment. Like the LED replacement of fluorescent bulbs, LEDs are anticipated to be an ecologically benign alternative technology. The efficiency of UV LEDs is now lower than that of low-pressure mercury lamps, notwithstanding their rapid annual improvement. Because no substitute technology has been developed, low-pressure mercury lamps are thus excluded from the RoHS Directive for particular uses until February 24, 2027 (Item 4(a)). If it is shown that no substitute technology is available beyond 2027, this exemption may be extended. Is an extension really required? Some applications may adopt LEDs right now, according to Nichia, and almost all applications will be able to do so by February 2027.
Here, Nichia presents a real-world example where UV LEDs are being explored as a disinfection alternative to low-pressure mercury lamps.
Surface disinfection using low-pressure mercury lamps → Case Studies of LED Adoption
Surface disinfection, air disinfection via purifiers, and water and sewage system disinfection are all included in the area of UV disinfection utilizing low-pressure mercury lamps. The cleaning of food industry equipment and containers is a common instance of surface disinfection. In food processing facilities, containers are filled with food after being exposed to UV light to disinfect the inside and stop germs from growing and contaminating the food.
An illustration of food containers exposed to UV radiation:
Low-pressure mercury lamps emit ultraviolet light from above the containers to disinfect the inside of many food containers at once. Fused quartz must therefore be used to cover low-pressure mercury lamps to prevent mercury contamination and glass breakage in the event that the lamp fails.
An illustration of radiation seen from above:
In contrast to low-pressure mercury lamps, LEDs may be used to irradiate just the target item with UV light since their configurations and positions can be accurately chosen and altered, as shown in the irradiation picture above. On the other hand, low-pressure mercury lamps emit light in all directions, exposing the spaces between individual containers and the lamps' backs to extra UV light.
Furthermore, since low-pressure mercury lamps take a long time to switch on and off, they must be kept "on" at all times. LEDs, on the other hand, provide instantaneous on/off, meaning that they may only be turned on when needed, potentially lowering energy use and CO2 emissions.
In light of the aforementioned information, the results of a comparison between LEDs and low-pressure mercury lamps are shown in the following table.
Study result
The input power needed to get the same disinfection effect in the real values in this research example is 600W and 312W.
Nichia's UV LED 434C was used to test the LED's irradiance and efficiency.
According to Shikoku Electric Power CO., Inc., the CO2 emission factor for FY2021 is 0.527t/MWh.
Compared to LEDs, which have an efficiency of 5.4%, low-pressure mercury lamps have a greater efficiency of 22%. However, LEDs may use up to 90% of the UV irradiation they generate, while low-pressure mercury lamps only use 9%. Thus, compared to low-pressure mercury lamps, which need 600W of electricity to provide the same disinfecting effect, LEDs require 312W. Furthermore, LEDs can only be activated when required. For example, if low-pressure mercury lamps are left on for 18 hours a day, LEDs can be turned on for 14 hours. Assuming that each lamp is used for 300 days, the power consumption of low-pressure mercury lamps with 600W of input power is 3.2MWh annually, whereas LEDs with 312W of input power consume 1.3MWh annually, a 60% reduction. Additionally, CO2 emissions are computed using the CO2 emissions of 0.527 tons per 1 MWh of power. LEDs produce 0.69 tons of CO2 annually compared to 1.7 tons from low-pressure mercury lamps, which is a 60% decrease.
Roadmap
Summary
The characteristics of LEDs, such as their high radiant flux utilization via selective illumination of just the required regions and their instantaneous on/off capabilities, were used in this case study to achieve notable advantages. Nichia can therefore unequivocally show that LEDs may serve as a substitute technology for mercury lamps with low pressure.
Apart from the aforementioned example, Nichia will collaborate with its clients and partners to create designs that use LED characteristics in other disinfection applications, such as air and water disinfection. Nichia will make every effort to ensure that LED technology replaces low-pressure mercury lamps.
Additionally, as the roadmap states, UV LED performance has significantly improved in recent years. Technological progress is fast because to the synergistic impact of development expectations for LEDs resulting from environmental restrictions and the need to battle infectious illnesses. In some instances, the use of LEDs in place of low-pressure mercury lamps is already being accomplished via the development of a design that capitalizes on LED capabilities. According to Nichia, this, together with the impressive enhancement of UV LEDs' fundamental performance, will cause an even bigger trend, and UV LEDs will be widely accepted as a substitute for low-pressure mercury lamps in all disinfection applications and domains. Consequently, there will be no need to extend the RoHS exemption beyond 2027.
In addition to working to address societal concerns including the establishment of a mercury-free and carbon-neutral society, Nichia will keep enhancing the performance of LEDs.
