When the white LED is operated at 100 ° C, the luminous efficiency is only reduced by about 3%. It is required that the white LED has "temperature stability" in order to make the luminous efficiency not greatly change under actual use environment. The luminous efficiency of the white LED directory value is mostly measured by applying a pulse current at an ambient temperature of 25 °C. At this time, the temperature (joining temperature) of the light-emitting portion of the blue LED chip was about 25 °C. However, when actually used in a product, the bonding temperature rises to 85 to 100 °C. In ordinary white LEDs, the luminous efficiency after temperature rise is reduced by 10 to 15% compared with that at 25 °C. Among some of the latest products, there have been varieties that suppress changes in luminous efficiency. For example, Philips Lumens' white LEDs for lighting use have a luminous efficiency that is only about 3% lower than that at 25 °C at a junction temperature of 100 °C. In order to improve heat dissipation, the LED chip is flip-chip packaged on a ceramic substrate, and a quantum well structure or the like is used to reduce the influence of temperature on the internal quantum efficiency. Sharp's white LEDs for lighting, which began shipping in March 2011, have a relatively small change in luminous efficiency with temperature (Fig. 1). Although the input power is as high as 25 W, it is difficult to lower the bonding temperature. However, when the white LED surface temperature (case temperature) is 70 ° C, the luminous efficiency and luminous flux are only reduced by 5 to 6 percentage points compared with the case of 25 ° C. The company said it will control the decline to about half compared to other companies' equivalent products. Higher temperature stability is achieved by using a fluorescent material whose performance changes little with temperature. The "Color Rendering Index" is an important indicator based on the wide application of white LEDs as a general lighting source. The purpose is to not create a sense of discomfort with the original light source. Previously, the color rendering index of white LEDs was mostly based on the average color rendering index (Ra). However, as the situation for lighting applications increases, only Ra is no longer satisfactory, and a higher special color rendering index, such as red and green with higher chroma, is required. Home Solar Energy Power System,Monocrystalline Solar Panel,Mini Solar Panel Generator,Solar Panels For Outdoor Guangzhou Fengjiu New Energy Technology Co.,Ltd , https://www.flashfishbatteries.com
Figure 1: Temperature dependence of weakening the performance of fluorescent materials