How to benchmark the UVC LED

A new metric from ams Osram aids the evaluation of UVC sources.

BY ALEXANDER WILM FROM AMS OSRAM

The deployment of UVC LEDs is on the up, with sources increasingly appearing in disinfection and treatment systems across consumer, professional, and industrial markets. As uptake expands, design engineers face more decisions relating to the specifications of the emitter, such as having to weigh up the importance of optical output, efficiency, wavelength, lifetime behaviour and cost. While datasheets list many of these parameters, designers still lack a single figure-of-merit that consolidates them into an application-relevant basis for comparison. This omission matters, complicating component selection, reducing transparency in technology benchmarking, and delaying optimisation, both at the source and system level.

A multi-dimensional decision
To illustrate the challenge associated with selecting an optimal UVC LED for a particular application, let’s consider this situation when trying to identify the best device for disinfection. The process begins by defining disinfection objectives, such as target dose, required reduction level and exposure geometry, and aligning all of them with the system constraints – they may include available electrical power, the thermal environment, form factor, safety and regulatory requirements,
and expected operating profile. Only once that task is completed is there a context for evaluating an appropriate balance of technical performance and cost.

Within a typical UVC LED, there’s much variety – differences in radiant flux levels, efficiencies, forward voltages, wavelengths, package types, and reliability classes – with each product potentially optimised for a distinct set of system conditions. However, while this variety is beneficial, it hampers comparison. For example, two LEDs may look similar when judged by just one parameter, but behave very differently, reflecting their full set of attributes.

The Cost of Germicidal Energy (CGE) may be viewed as the total cost over life (device + energy), divided by total germicidal-weighted optical energy delivered over that life in a dedicated system setup.

Due to this, when selecting the most appropriate UVC LED for a particular task, trade-offs are inevitable. A common one is that of efficiency versus cost, as higher efficiencies trim running costs, but may carry a higher price tag. Another matter to consider is lifetime versus output. Cranking up the drive current boosts the optical output of a UVC LED in the short-term, but accelerates degradation unless effort is directed at a superior thermal design. There’s also the need to consider effectiveness at different wavelengths, as the germicidal effect varies, due to wavelength-dependent action spectra.

One may argue that having a decision-making process that evaluates a range of characteristics is hardly unique to the UVC LED. However, when selecting this particular device there are significant consequence at the system level, due to differences in delivered dose, spectral weighting, and degradation behaviour impacting performance margins and the cost over the product’s life.

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Installations for disinfection of water with ultraviolet radiation.

Traps for the unwary
In consumer applications, decisions are often dominated by one or two parameters, and it’s possible to enjoy an acceptable basic performance while prioritising low component costs. Under these circumstances, it can be enough to simply rank products by their purchase price or nominal radiant power.

It’s a different ball game for professional applications. Here, the decision space is more complex. System operation is often either continuous or long-duration, and the source cost, electrical energy consumption and lifetime may govern the total-cost-of-ownership and maintenance strategy. So, it may be misleading to compare LEDs with a single parameter, as the ‘best’ option depends on how parameters interact at a certain operation point.

Helping the decision-making process are visualization methods, such as a spider (radar) chart. They help to consider multi-parameter data, by communicating differences at a glance. But these charts tend to be descriptive, rather than quantitative: they don’t incorporate parameter interactions, they don’t reflect how parameters translate into delivered germicidal performance, and they often fail to convert performance into economic outcomes. Due to these limitations, while they may support early-stage screening, they are less suited to providing the primary decision basis for optimising professional or industrial systems.

A new benchmark
To provide a consolidated basis for comparison, our team at ams Osram has introduced a unified metric for UVC sources: the Cost of Germicidal Energy (CGE). This yardstick expresses the cost required to deliver a defined amount of germicidal-effective UV energy over the usable operating life of a source. It considers the source lifetime, which is the time it takes for the radiant flux to fall to a specified maintenance threshold or lifetime criteria, and ties this to a flux maintenance criterion – it might be an RxxB50 lifetime, which is the lifetime criteria at which 50 percent of LEDs are still above the specified performance limit of xx percent. The key implication is that performance is represented over time rather than at initial operation only.

One of the great strengths of CGE is that it integrates all the key technical and economic parameters into a single indicator. Included in the CGE is the: source cost, which is the purchase cost per UVC source; the energy cost, considered as the cumulative electricity cost over operating life; the lifetime and flux maintenance, defined as the operational duration until output declines to a defined maintenance threshold used in the CGE normalisation; the system efficiency, a figure that accounts for system-level losses, such as optical coupling efficiency, beam shaping and target geometry; and the germicidal-weighted radiant flux. The latter is the radiant output, weighted by an action spectrum (standardised, such as IESNA 2000b, or organism-specific, such as MS2), accounting for wavelength effectiveness and spectral power distribution, and scaled to the flux maintenance limit defined by the RxxB50 lifetime value.

Conceptually, the CGE can be understood as the total cost over life (device + energy), divided by total germicidal-weighted optical energy delivered over that life in a dedicated system setup.

When using our new metric, it’s easy to compare LEDs with different wavelengths, efficiencies, and lifetime behaviours, because differences are converted into a common, application-relevant quantity: the cost per germicidal-effective energy. In addition, the CGE enables comparison across technology classes when equivalent assumptions are used, such as electricity price, maintenance threshold, and action spectrum selection.

Supporting engineering decisions
While a single metric will never replace detailed engineering analysis, it can improve decision workflow on a number of fronts. They include providing an objective ranking under defined assumptions, with CGE providing a consistent basis for comparing candidates when system requirements are fixed and assumptions are documented. In addition, there’s: sensitivity insight, as by evaluating how CGE changes when parameters vary, it becomes clearer whether cost, efficiency, lifetime, or spectral effectiveness is the dominant driver in a given application context; and there’s roadmap guidance – CGE can highlight which parameter improvements deliver the largest economic impact, supporting prioritisation in LED development and packaging innovation.

It should be noted that just because one decides to use the CGE metric, that does not prevent them from using additional metrics. When working with a variety of metrics, CGE acts as a unifying ‘headline number’, complementing detailed specifications and application constraints.

To system-level comparisons
When the CGE also incorporates and considers the system efficiency of UVC fixtures, the comparison naturally extends from source-level to system-level evaluation. In this form, CGE can compare complete UVC solutions – including different source technologies – because it accounts for how effectively each system converts electrical energy and component cost into germicidal-effective energy delivered to the target.

This capability for higher-level evaluation is particularly powerful when the system architecture strongly influences performance – that’s the case in air and surface treatment, where optical control and directionality play a significant role; and in water treatment, where key factors include reactor geometry, hydraulic design, and UV utilisation. By including system efficiency, the CGE metric ensures that a number of advantages are accounted for, such as improved photon utilisation through tailored optics, reduced losses, and better irradiation of the treatment target within the same unified framework.

Thanks to this merit, the CGE is not just a tool for component selection. In addition, it’s also a basis for comparing end-to-end system concepts on a common economic and performance axis.