Addressing design issues when working with UVC LEDs: Page 2 of 4

November 19, 2015 //By Hari Venugopalan
Addressing design issues when working with UVC LEDs
Hari Venugopalan, Director of Global Product Management, Crystal IS considers the design issues likely to be faced when working with UVC LEDs.
strength is directly proportional to light intensity. The excitation power depends on the trace concentration levels that need to be detected, so in these applications the light output required from a single LED can be greater than 2 mW. Figure 1 shows the irradiance comparison between common UV light sources in instrumentation. Although the input power is much less for the LED, the irradiance at the desired UVC wavelength is higher than the other sources making it a more efficient light source for the specific measurement.

Figure 1 This graph compares the irradiance of a UVC LED, xenon flash lamp, and deuterium lamp.

After wavelength and light output are selected, another important parameter is the viewing angle as it impacts the instrument optical train. Broadly, there are two options – narrow or wide angle. The former is achieved with a ball lens, the latter with a flat window. The narrow viewing angle allows for high intensity of light available over a small area. This package type is typically used when directly focusing the light into the instrument.

A flat window package has a wider radiation pattern that has a greater tolerance in alignment with fiber for remote coupling. It is particularly useful in applications where the flow cell must be isolated from the light source and electronics, like in monitoring high temperature chemical processes or in chromatography with highly volatile solvents. When practical, a narrow angle ball lens can keep components in the instrument to a minimum, while the flat window provides enhanced flexibility in design.

Optimizing the drive current allows the designer to balance the light output with the lifetime requirements of the application. Driving an LED below the manufacturers rated current will decrease the light output, but it will also increase the lifetime of the light source. In applications that require a high LED output power, some end users choose to operate LEDs at an elevated current above

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