Analysis of the physical and microbiocidal characteristics of an emerging and innovative UV disinfection technology

IntroductionSurface disinfection is one of the key points to reduce the risk of transmission both in healthcare and other public spaces. A novel UV-chip disinfection technology is presented. Technological, photonic and microbiocidal characteristics are evaluated taking as reference an ultraviolet-C (UV-C) LED source of equivalent radiant power.MethodsThe UV chip has a circular radiating surface with a diameter of 1.3 cm, emitting UV cold light at about 5 mW and driven current of about 80 µA. Four bacterial strains were used to conduct the microbiological tests at 4°C and 60°C to evaluate the bactericidal performance of the two technologies under the same operating conditions.ResultsSpectral differences were found between the UV-C LED and the chip, with an emission curve strictly around 280 nm and a broader band centred around 264 nm, respectively. Between-technology microbiological inactivation levels were comparable, achieving total abatement (99.999%) in 8 min at 7.5 cm.DiscussionThe UV chip exhibits unique properties that make it applicable in some specific contexts, where UV-C LEDs present the most critical issues. Besides, it is portable and exhibits a broad spectrum of UV wavelengths with a peak where the maximum microbiocidal efficacy occurs. Important issues to be addressed to improve this technology are the high voltage management and the too low energy efficiency.ConclusionThis cold emission technology is virtually unaffected by changes in ambient temperature and is particularly useful in short-distance applications. Recent developments in technology are moving towards a progressive increase in the chip’s radiant power.

Relationship Between the Cost of 12 Light-curing Units and Their Radiant Power, Emission Spectrum, Radiant Exitance, and Beam Profile

SUMMARY Objectives: To correlate the radiant power (mW), radiant exitance (or tip irradiance in mW/cm2), emission spectrum (mW/cm2/nm), and beam irradiance profile of 12 light-curing units (LCUs) available in the Brazilian market with their market cost. Methods and Materials: Six LCUs that cost more than US$900 (Bluephase G4,VALO Grand, VALO Cordless, Radii Xpert, Elipar DeepCure-S, and Radii plus) and six low-cost LCUs costing less than US$500 (Radii Cal, Optilight Max, High Power LED 3M, Emitter D, Emitter C, and LED B) were examined. Radiant power (mW) and emission spectrum (mW/nm) were measured using an integrating sphere connected to a fiber-optic spectroradiometer. The internal tip diameter (mm) of each LCU was measured using a digital caliper and was used to calculate the average radiant exitance (mW/cm2). Irradiance profiles at the light tip were measured using a commercial laser beam profiler. The cost of each LCU in Brazil was correlated with internal tip diameter, radiant power, and tip irradiance. Results: None of the low-cost LCUs were broad spectrum multiple peak LCUs. There was no correlation between the cost of the LCUs and their averaged tip irradiance; however, there was a high positive correlation between the cost of the LCUs and the radiant power and tip diameter. The VALO Grand, Elipar DeepCure-S, VALO Cordless, and Bluephase G4 all emitted a higher radiant power. They also had a significantly greater tip diameter than other LCUs. For the LCUs with a nonuniform output, some areas of the light tip delivered less than 400 mW/cm2, while other areas delivered more than 2500 mW/cm2. Conclusions: In general, LCUs that had a higher cost (US$971-US$1800) delivered more power (mW) and had a greater tip diameter (mm), which covered more of a tooth. In general, the low-cost LCUs (US$224-US$470) emitted a lower radiant power and had a smaller tip diameter.

Supercontinuum laser-based monochromatic radiant source for detector spectral responsivity characterization in the range 0.9–1.6 μm using absolute cryogenic radiometer

An improved monochromatic radiant source with spectral bandwidth of 4 nm based on supercontinuum laser and a double monochromator was included in absolute cryogenic radiometer-based facility to improve the accuracy of spectral responsivity measurement in the range 0.9–1.6 μm. The developed feedback system ensures stabilization of monochromatic radiant power with standard deviation up to 0.025 %. Radiant power that proceeds detector under test or absolute cryogenic radiometer varies from 0.1 to 1.5 mW in dependence of wavelength. The spectral power distribution of its monochromatic source for various operating mode is presented.

Study on Reabsorption Properties of Quantum Dot Color Convertors for Light-Emitting Diode Packaging

Quantum dot (QD) attracts great attention in light-emitting diode (LED) packaging for high-quality light sources, while it leads to low light efficiency due to the significantly high reabsorption loss between QDs. Accordingly, we experimentally study the reabsorption properties of QD color convertors (QCCs) for LED packaging considering various thicknesses and concentrations under different injection current. The results indicate the QCC configuration with a small thickness and large concentration can have the same absorption ability for chip light as that with the opposite configuration, resulting in the same QD light proportion. However, the QCC configuration having smaller thickness is more useful to decrease the reabsorption loss, leading to higher radiant power (an increase of larger than 37.2%). Moreover, it is essential to gain a high radiant power of QD light with small reabsorption loss, which can be realized by combining QCCs with a low QD content and a source with a large injection current. Based on this simple and effective approach, a conversion loss smaller than 20%, close to their quantum yield, can be achieved, which is approximately four times smaller than that gained by QCCs with a high QD content. However, it introduces additional radiant power of chip light, suppressing further improvement in the QD light proportion. Much work is still required to make full use of the redundant chip light. This study provides a better understanding of the reabsorption properties of QCCs and can significantly accelerate their applications in illumination and display applications.

Measurement of the absolute spectral responsivity in the mid-infrared based on the cryogenic electrical substitution radiometer and an optimized thermopile detector

The Physikalisch-Technische Bundesanstalt (PTB) expanded its capabilities of the absolute measurement of radiant power to the spectral range of the mid-infrared (MIR) by implementing additional MIR laser radiation sources at one of the PTB's cryogenic electrical substitution radiometer facilities. This extension enables absolute calibrations of the spectral responsivity of detectors in the MIR traceable to the International System of Units (SI). The thermopile detector TS-76 was characterized and calibrated in view of its spectral responsivity s(λ) in the wavelength range between 1.5 and 10.6 µm at the expanded cryogenic electrical substitution radiometer facility. The relative standard measurement uncertainty was significantly reduced to 1.4 % by developing an optimized and thermally stabilized detector housing design. The TS-76 was established as a mid-infrared transfer detector for the SI traceable measurement of radiant power and the dissemination of the spectral responsivity s(λ) in the MIR.