Radiometric analysis of UV to near infrared LEDs for optical sensing and radiometric measurements in photochemical systems

Abstract

LEDs have been established as light sources in countless areas of optical sensing and chemical analysis, where they offer a better alternative to traditional light sources in terms of low-cost, small size and robustness supporting portability, and performance parameters such as low noise. However, the lack of rapid, facile and accurate radiometric analysis of LEDs is a major limiting factor which constrains their purposeful use. Therefore, here we present comprehensive radiometric analysis of LEDs in terms of absolute emission spectra, radiometric power output, irradiances, radiant efficiencies as well as uncertainties. This allowed us to develop and cross-validate a rapid, facile, accurate and low-cost radiometric analysis of LEDs with directional light output using a large active area silicon photodiode in a simple optical design with the LED light source in proximity, without the need for a calibrated light source. We demonstrate that data for a wide range of 21 commercial LEDs in UV, vis and NIR spectral range (255–950 nm) agree very well with two entirely independent approaches. First, we obtained an excellent agreement with accuracy within 5% for radiometric power output measured using chemical actinometric methods. Further, we obtained irradiance (mW/cm2) and radiant efficiency values (%) for the LEDs. The accuracy of irradiance measurement was within 2% when compared with a spectrophotometric method based on a radiometrically calibrated spectrophotometer. The measurement uncertainty at 95% confidence level for values of radiometric power output were reduced 3-fold compared to the existing techniques. We also demonstrate that this facile, accurate and low-cost radiometric analysis can be further extended to accurately measure quantum yield of photochemical reactions and fluence values in actinometric systems.