Technology comparisons
Mercury vapor lamps in various iterations (medium- and low-pressure) have been at the core of UV disinfection for several decades. Although the use of LEDs in the mass visible light market have become commonplace during the last decade, their use in the disinfection arena was initially restricted to specialized niche applications due to relatively high cost and limited UV output efficiency. In recent years, great strides have been made in refining UV-C LED technology to the point where the cost-benefit analysis has become more favorable, firstly in POU applications (e.g., water dispensing) and, most recently, in POE applications. The early negative aspects of material toxicity, heat management, and cost have been addressed. All materials used are now reduction of hazardous substances (RoHS)-compliant, integrated heat sinks handle thermal management effectively and continuously improving cost versus output is well demonstrated by the graphical representation of Haitz’s Law (see Figure 1). Haitz’s law is the observed and forecasted improvement of LEDs over the years. This law has found that every decade, the cost falls by a factor of 10 and the amount of light generated increases by a factor of 20. This evolution is taking place at the same time that pressure to eliminate the use and subsequent disposal of mercury is increasing.
At their core, UV disinfection systems are based on two principles – the efficiency of the UV lamp and the efficiency of the reactor design. Typically, conventional UV lamps are more efficient, producing more UV light than heat when compared to UV-C LED light sources. The opposite is true with conventional mercury lamp reactor design, as the cylindrical design is typically less efficient than modern UV-C LED reactors, which can be custom-designed based on the flexibility of the LEDs. In addition to the cost versus output improvements noted above, UV-C LED reactor and UV output efficiency are both benefitting from continuous improvement at a rapid pace, accelerating the penetration of LED technology into higher-flow applications. A particular advantage offered by UV-C LED technology is the ability to tailor UV wavelengths for specific, targeted applications due to not being constrained by the 254nm output of low-pressure mercury vapor lamps.
While conventional mercury-lamp-based UV disinfection systems will continue to dominate some sectors of the market, more especially high-flow commercial and industrial applications, there are additional factors (such as cost of ownership and long-term maintenance requirements) that will drive the adoption of UV-C LED devices in a growing number of applications. Due to the unique properties of uv-c leds, fouling is much less of a concern as heat discharge is managed at the back of the system using heat sink technology rather than the quartz lamp/sleeve/ water interface, where fouling and consequent reduced UV transmission can occur in water containing hardness minerals. In conventional systems, instant -on LED technology allows for powering the LEDs only when water is flowing, thereby eliminating the heat build-up that results in fouling during stagnant (no flow) conditions often found in systems using permanently powered mercury lamps. Elimination of the familiar hot water shot associated with conventional systems not equipped with a temperature management dump valve is an added benefit. The instant on/off properties of LEDs and consequent ability to be powered only when needed drastically reduces lamp replacement intervals when compared with conventional mercury lamps. Based on average household water demand of 2-3 hours per day, the replacement interval for LEDs is typically five years, compared to annual replacement of mercury lamps. The on demand advantage, together with flow regulated power demand, means that the long-term electrical energy requirement is substantially lower for UV-C LED systems.
