Ultra-violet (UV) light is found between the visible and x-ray spectrums. The wavelength range is specified as 10-400 nm, although several optoelectronic companies consider a wavelength as high as 430 nm as UV range. UV light is named due to the "violet" color it generates in the spectrum’s visible portion, however a major portion of UV light is not visible to the human eye (Figure 1).
Figure 1. Color spectrum highlighting UV-A, UV-B, and UV-C
Over the last couple of years the demand for UV LEDs has grown tremendously. This is due to the technological advances in manufacturing solid-state UV devices, and the growing demand for environmentally friendly techniques of generating UV light. The UV LEDs available currently in the optoelectronics market have a wavelength range of 265 - 420 nm, and various package styles such as; surface mount, through-hole, and Chip-On-Board (COB). UV LED emitters can be used in numerous applications, but each application is relies on output power and wavelength. UV light for LEDs can be split into three general areas - UV-A, UV-B and UV-C, as listed in the following table:
||400 - 315 nm
||315 - 280 nm
||280 - 100 nm
"Upper" UVA Type Devices
The "upper" UVA type devices have been available since the late 1990s. Conventionally these LEDs are used in applications such as; counterfeit detection or validation (documents, currency, and driver's license) and forensics. These applications require very low power output, and the actual wavelengths used are in the 390 - 420 nm range. These types of LEDs are now readily available from different sources, and have the lowest cost of all UV products.
"Middle" UVA LED Component
The "middle" UVA LED component area has seen tremendous growth over recent years. Most of the applications in the 350 - 390 nm wavelength range are for UV curing of industrial and commercial materials, such as coatings, adhesives, and inks. LEDs offer benefits over conventional curing technologies, such as fluorescent or mercury, due to the minimal cost of ownership, increased efficiency, and system miniaturization. The use of LEDs for curing is increasing as the supply chain is pushing the adoption of LED technology. Currently the costs of this wavelength range are much higher than the upper UVA area, but a rapid progress in manufacturing, as well as increasing volumes, are gradually reducing the prices.
"Lower" UVA and "Upper" UVB Ranges
Recent introductions into the market are "lower" UVA and "upper" UVB ranges of about 300 - 350 nm. These devices have the potential to be used in numerous applications, such as UV curing, DNA analysis, biomedical, and many types of sensing. There is a major overlap in all three of the UV spectral ranges, so users need to consider what is suitable for the application, and the most cost-effective - generally the lower the wavelength, the higher the LED cost.
"Lower" UVB and "Upper" UVC Ranges
The "lower" UVB and "upper" UVC ranges of about 250 - 300 nm is yet to be fully explored, although the demand for this product in water and air purification systems is growing. Very few companies manufacture UV LEDs in this wavelength range currently, and even less are able to manufacture products with an adequate lifetime, performance characteristics and reliability. The cost of devices in the UVC/B range continue to be very high and may be unaffordable in certain applications. In 2012 the first commercial UVC LED based disinfection system was introduced and since then, many companies began to seriously pursue LED based products.
A general concern with UV LEDs is any potential safety risks. A commonly used and well-known source for generating UV output is the "black light bulb". For years it has been used to produce a fluorescence or glowing effect on detailed types of posters and other applications, such as verification of currency and paintings. These bulbs are generally within the "upper" UVA spectrum, with relatively low energy. This region of the UVA spectrum is considered the safest of the various spectra of UV light, although high exposure has been attributed to skin cancer in humans and issues such as rapid skin aging.
Compared to standard incandescent or fluorescent type bulbs, LEDs are not only highly directional, but have very narrow viewing angles. Directly viewing a UV LED is not advisable as it can harm the eyes. The UVC and UVB ranges are used for germicidal and sterilization requirements. Light generated at these wavelengths is harmful to micro-organisms as well as humans.
These LED lights have to be shielded at all times and should not be viewed with the naked eye. Exposure to these wavelengths could result in skin cancer and temporary or permanent vision loss. Marktech Optoelectronics offers all UV devices with warning labels (Figure 2). Customers buying a UVC or UVB LED must also sign a document stating that they understand the risks, and will take adequate precautions regarding the use and handling of these products.
Figure 2. All UV devices should have warning labels
This information has been sourced, reviewed and adapted from materials provided by Marktech Optoelectronics.
For more information on this source, please visit Marktech Optoelectronics.