Concerns related to the novel coronavirus in 2019/20 seem to have driven significant interest in the use of ultraviolet (UV) emitting LEDs for antimicrobial/germicidal applications. While light in the UV spectrum (particularly in the UV-C band) is demonstrably useful for this purpose, LEDs are presently very limited in their feasibility as a source for such outside a rather narrow scope.
The reasons for this are two-fold. First, the UV-C LEDs available at the time of writing are about as effective at turning electricity into UV light as traditional incandescent lamps are at turning it into visible light. Both only convert about 1-2% of the electrical energy applied to them into light of the desired form. Second, the total amount of UV energy that can be generated by a single UV LED is on the order of 100 to 1000 times less than that which is available from other UV-C production technologies, which are generally between 10 and 30 times more efficient than currently-available LEDs in terms of converting an electrical input into UV radiation. Simply put, today’s UV-C LEDs can only generate a miniscule amount of UV light, and require a relatively large amount of electrical energy to do it.
Developments in LED technology for visible lighting applications have advanced rapidly in the past 10-15 years, developing from an expensive, weak, and largely unappealing option to one that is widely preferred. Given this remarkably rapid advancement in LED technology for visible lighting purposes, it’s understandable that many would assume that UV-emitting LEDs are similarly well-developed and advantageous. Unfortunately, this is not the case.
Consider for example the XST-3535-UV (one of the more powerful UV-C LEDs carried by Digi-Key at the time of writing) annotated excerpts from the datasheet for which are below. Operated at the nominal 350mA drive current for the device, nearly 2.3 watts of electrical energy go in, but only about 0.055W of which (at best) comes out in the form of UV light. Compare this with the excerpt from a Philips Lighting UV-C product catalog, showing data for a line of fluorescent-style UV-C lamps; here a device consuming 20 watts of electrical input can generate 6 watts of UV output; a 30% conversion efficiency. The latter device generates over a hundred times more UV, and does so upwards of ten times more efficiently.
When used for germicidal purposes, the dose of UV-C radiation required to disable >99% of a given pathogen on a flat, smooth surface is cited by various sources as being on the order of 5 to 50mJ/cm2, varying widely depending on the germ of interest and other factors. Stated differently, under ideal conditions a UV LED such as the one referenced above might be able to do a reasonable job of disabling most of the microbes on one side of a postage stamp in around 5 seconds. By the time one considers an area the size of a common 8.5x11” piece of paper, that figure rises to around 10 minutes. Other factors (such as actually getting an emitter to cast UV light on the desired surface instead of off to the side) can frustrate matters.
In summary, UV LEDs are potentially useful tools for antimicrobial purposes in applications involving small surfaces, where rapid action is not necessarily required, and where treated surfaces can be isolated from human exposure during the treatment process. It should be noted that UV radiation of a character useful for germicidal purposes implicitly poses a hazard to humans; if it’s potent enough to do damage to germs, it’s potent enough to damage cells in the human body.
Because most consumers have neither the tools nor skills needed to objectively measure the effectiveness of a given germicidal agent, there is ample opportunity for unscrupulous or well-intentioned yet ill-informed actors to take advantage of widespread concerns regarding environmental pathogens, by selling ineffective products to people who lack the ability to determine whether they’re effective or not. Be advised that most products containing a few LEDs and offering hope of safety or protection from disease with a quick wave of a magic wand are likely of this sort.