Abstract
Constant light power operation of an ultraviolet (UV) LED based on portable low-cost instrumentation and a monolithically integrated monitoring photodiode (MPD) has been reported for the first time. UV light irradiation has become one of the essential measures for disinfection and sterilization. Monitoring and maintaining a specified light power level is important to meet the criteria of sterilization. We built a module composed of a monolithically integrated UV LED and MPD, a transimpedance amplifier, an Arduino Uno card, a digital-to-analog converter and a Bluetooth transceiver. An Android App that we wrote remotely controlled the UV LED module via Bluetooth. The Arduino Uno card was programmed to receive demands from the smartphone, sent a driving voltage to the LED and returned the present MPD voltage to the smartphone. A feedback loop was used to adjust the LED voltage for maintaining a constant light output. We successfully demonstrated the functioning of remote control of the App, and the resultant UV LED measured power remained the same as the setting power. This setup can also be applied to visible or white LEDs for controlling/maintaining mixed light’s chromaticity coordinates or color temperature. With such controlling and internet capability, custom profiling and maintenance of precision lighting remotely would be possible.
Highlights
In the year 2020, we reported the on-chip power monitoring of UV light-emitting diodes (LEDs) utilizing a sapphire substrate as a slab waveguide, which coupled part of the emission power towards a monitoring photodiode (MPD) shaped in a loop surrounding the UV LED [17,18]
(On-chip power monitoring was insensitive to ambient lighting.) The smartphone’s screen showed a measured MPD voltage of 1.32 V and a present UV LED light power of 2.0 mW, when the setting light power was 2.0 mW
The bottom line on the screen was the place to upload a new UV LED light power, which was restricted in the range of 1.5–3.0 mW in this demonstration, because the UV LED was mounted p-side up, having a sapphire substrate of poor thermal conductivity
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. None of the above-mentioned photodetectors were used for monitoring the surface-emitting power output of the integrated LEDs. In the year 2020, we reported the on-chip power monitoring of UV LEDs utilizing a sapphire substrate as a slab waveguide, which coupled part of the emission power towards a monitoring photodiode (MPD) shaped in a loop surrounding the UV LED [17,18]. Yin et al reported monolithically integrated photodiodes in white LEDs to monitor the fluctuation of light intensity over time [19]. They studied the effect of various MPD locations on the light intensity distribution of the LED and concluded that a central location was the best.
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