The Emergence of the UV LED

Ultraviolet LEDs are commercially available, but the technology is 15 or more years behind their visible counterparts.

In my last piece, I mentioned that I am working on several UV projects. Here is a little background on the UV LED landscape now.

The ultraviolet region of the electromagnetic spectrum is immediately adjacent to the visible spectrum. It covers a wide range, from 100 to 400 nm, and is subdivided into UV-A (315-400 nm, the closest to the visible region), UV-B (280-315 nm), and UV-C (100-280 nm). Ultraviolet radiation performs many beneficial functions. It is used in curing, dental, medical, and sterilization applications, and in tanning salons. The UV-A from the sun that reaches the earth's surface helps our bodies produce vitamin D.

The legacy artificial UV sources are similar to the legacy visible light sources. A very high percentage of them are fluorescent tubes. So naturally, LEDs have the potential to offer the same benefits in the UV realm as they do in the visible: namely, increased reliability, power savings, and freedom from mercury and other hazardous substances.

Innovator stage

UV LEDs are far behind their visible cousins on the product life-cycle curve. As the photonic energy levels increase, it becomes accordingly more difficult to produce the respective LED source. Red LED's, with their relatively long wavelengths, have been around since the late 1950s, whereas the much shorter wavelength blue wasn't available until the 1990s.

Commercially available UV LEDs have recently entered the market. They are still in the innovator stage, at best the early adaptor stage, and have the stratospheric pricing that goes with that end of the product life-cycle curve. UV LED performance and "lumen maintenance" are more or less at the same stage as the visible LEDs were in the mid-1990s. There are no UV LED standards.

Who's who

When I first started working with UV LEDs, I expected to see familiar names among the suppliers. After all, an LED is an LED, right? Not so. Save a few, the names are different. The traditional LED suppliers that do offer UV LEDs include Nichia, LG Innotek, and, joining the fray just recently, Philips LumiLEDs (sponsor of this site). Other companies supplying UV LEDs include LED Engin, OSA Opto, Sensor Electronic Technology (SETi), and Crystal IS.

Safety

Today's visible LEDs can create high enough flux to raise health concerns. It is not wise to look directly at any of today's high-flux devices, but even if you do, there is a natural tendency to avoid prolonged exposure, because it's just uncomfortable. The risk from UV LEDs can be much greater. By definition, save for some suffering from aphakia, UV radiation is invisible. It is possible to be near an operating source without knowing it. In sufficient doses, UV can lead to eye and skin damage. When I work with UV, I wear safety glasses (with known UV transmissions characteristics) and a long-sleeved laboratory coat. I generally add a visible LED to the chain so that it is obvious when power is on. I also try to minimize the time the sources operate.

Aside from the wavelength, UV LEDs are similar to visible LEDs in most other aspects. Metrics defining the UV sources parallel those of the visible spectrum. In the visible world we use illuminance (lumens per square unit surface area), luminance, luminous flux, and luminous intensity. The terms in the UV region (or actually anywhere on the electromagnetic spectrum outside of the visible region) become irradiance (Watts per square unit surface area), radiance, radiant flux, and radiant intensity.

Please share your experience working with UV LEDs in the comments.

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