Thermal resistanse and nonuniform distribution of electroluminescence and temperature in high-power AlGaInN light-emitting diodes, St. Petersburg Polytechnical
In studies of non-visual lighting effects conflicting results are frequently obtained. We suppose that such individual differences can be related to the initial functional state, as well as to the individual type of response to light exposure. This raises the question of the need to develop methods for express-diagnosis of functional state in response to a standardized light exposure. Our results show that the effect of fatigue during mental workload can be detected by measuring the critical flicker fusion frequency for light with the specific colors and brightness levels. However, the reliability of this method is difficult to estimate because of the different brightness of LEDs of different colors. We believe that the using of a "smart lighting" devices, allowing obtaining specific color and brightness by mixing individual colored LEDs, will overcome this limitation.
Keywords-non-visual effects of light; color flicker fusion frequency; LED; functional states; mental fatigue; smart lighting; physiological labilityI.
We report a technique which can simplify and improve the Infrared (IR) micro-thermography of light-emitting diodes (LEDs) by the use of a special thin-film coating which combines strong absorption in the wavelength range of sensitivity of IR microscope (2.5-3µm) and transparency in the visible region of the own LED radiation. As is well known, conventional IR temperature measurements, made on the LEDs, lead to significant difficulties and errors as consequence of the optical transparency of substrate/heterostructure layers and low emissivity of metalized contacts. The proposed method allows avoiding the time-consuming procedure of emissivity calibration for different materials forming LEDs, while increasing the measurement accuracy.
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