Abstract
The increasing demand for light emitting diodes (LEDs) is driven by a number of application categories, including display backlighting, communications, signage, and general illumination. Nowadays, they have also become attractive candidates as new photometric standards. In recent years, LEDs have started to be applied as wavelength-selective photo-detectors as well. Nevertheless, manufacturers’ datasheets are limited about LEDs used as sources in terms of degradation with operating time (aging) or shifting of the emission spectrum as a function of the forward current. On the contrary, as far as detection is concerned, information about spectral responsivity of LEDs is missing. We investigated, mainly from a radiometric point of view, more than 50 commercial LEDs of a wide variety of wavelength bands, ranging from ultraviolet (UV) to near infrared (NIR). Originally, the final aim was to find which LEDs could better work together as detector-emitter pairs for the creation of self-calibrating ground-viewing LED radiometers; however, the findings that we are sharing here following, have a general validity that could be exploited in several sensing applications.
Highlights
Light emitting diode (LED) development started in the early 1960s with the observation of infrared and red radiation emission, reaching blue wavelengths in the early 1990s [1] thanks to Akasaki, Amano, and Nakamura (Nobel prize winners, 2014), and is continuing deeper into the ultraviolet (UV)
The increasing applications of LEDs in photometry and radiometry, even as detectors, in addition to sources, has led to the study of various parameters of LEDs, which are relevant to radiometric measurements
The behavior of more than 50 LEDs was studied as sources and several of them as detectors, with the aim to begin filling the lack of data in manufacturers’ datasheets
Summary
Light emitting diode (LED) development started in the early 1960s with the observation of infrared and red radiation emission, reaching blue wavelengths in the early 1990s [1] thanks to Akasaki, Amano, and Nakamura (Nobel prize winners, 2014), and is continuing deeper into the ultraviolet (UV). To become the preferred light sources for many important applications, e.g., light sources in traffic signals [3], solid-state information and image displays [4], full-color illumination for back-lighting liquid crystal displays [5], automotive signaling and tail lights [6], instrument cluster displays [7], food production [8], analytical chemistry [9,10] microfluidics control [11] and, soon, in metrology as promising new photometric standards [12] In all of these applications, LEDs are used as sources, but, this is a more exploited LED property, it has been demonstrated that LEDs could be applied as radiation sensors with an intrinsic bandwidth-limited sensitivity related to the emission spectrum [13,14,15]. The technical details exposed in this article could be of help to the sensors community in the realization of low-cost detectors or matched source-detector couples in various applications
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