Abstract
We present a high-resolution non-contact method for the measurement of two-dimensional (2D) phosphor surface temperature distribution (PSTD) of phosphor-coated light-emitting diodes (pc-LEDs) based on advanced hyper-spectral imaging technology. The studied pc-LEDs with a surface-mounted device structure are mainly consisted of blue InGaN/GaN-based LED chips (with a spectral emission at about 456 nm), red (Sr,Ca)AlSiN3:Eu2+ phosphors (with a spectral emission at around 623 nm), and transparent silicone gels. Experimental temperature results are compared with those of micro-thermocouple (μ-TC) and infrared thermal imaging (TI), and fairly good agreements can be noticed. However, the spatial resolution of this proposed method is more than one order of magnitude higher than that of TI method, and the proposed method provides more detailed surface temperature information of phosphors than the latter. Therefore, we believe that this proposed method can serve as useful tools for the non-contact measurement of PSTD in pc-LEDs with or without optics lens.
Highlights
The phosphor-coated light-emitting diodes have been greatly applied in the general lighting, automobile lighting, and back-lighting of displays
We present a high-resolution non-contact method for the measurement of two-dimensional (2D) phosphor surface temperature distribution (PSTD) of phosphor-coated light-emitting diodes based on advanced hyper-spectral imaging technology
The spatial resolution of this proposed method is more than one order of magnitude higher than that of thermal imaging (TI) method, and the proposed method provides more detailed surface temperature information of phosphors than the latter
Summary
The phosphor-coated light-emitting diodes (pc-LEDs) have been greatly applied in the general lighting, automobile lighting, and back-lighting of displays. Thermal imaging is capable of detecting temperature distribution of pc-LEDs, but the emissivity of materials is hard to be determined, especially for phosphor/silicone mixtures with various mass ratios, and the inaccurate emissivity would affect final experimental results. Our research groups have conducted the measurement of 2D temperature distributions for GaN-based LEDs by the hyper-spectral imaging method [6], [7], and obtain the averaged phosphor temperature of pc-LEDs based on divisional normalized emission power of phosphors’ emissions [9] With these progresses, we can readily achieve high-resolution 2D phosphor surface temperature distribution of pc-LEDs. the calculated temperature results by proposed methods are compared with those of μ-TC method and TI method. The experimental setup for measuring 2D surface temperature distribution of pc-LEDs is schematically illustrated, including following components as: hyperspectral imager with charge-coupled device (CCD) detector, high-accuracy optical microscope, tested pc-LEDs (heatsink, aluminum substrate, blue LED, phosphor/silicone mixture), electrical source meters (Keithley 2400), and temperaturecontrolling systems (Whtalent TLTP-TEC). The structure of pc-LEDs belongs to surface-mounted device (SMD)
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