Lifetime Assessment of Polymethyl Methacrylate (PMMA) Plastic Lens, Used in LED-Based Products

Polymethyl methacrylate (PMMA) is commonly used as a lens or light guide plate in the lighting industry, and the working environment of high-temperature and high-intensity light causes it to fail to turn yellow or even deform. In order to study the performance degradation law and aging phenomenon of PMMA under the simultaneous action of light and heat, we performed accelerated photothermal aging tests on PMMA lenses at three color temperatures (3000 K, 4000 K, blue light) and ambient temperatures (65°C, 85°C, 105°C). The experimental results show the following: (1) After 1400 h of aging, the transmittance of the PMMA lens is significantly decreased at wavelengths below 500 nm. The comparative analysis of photothermal and thermal aging experiments shows that the photothermal coupling effect is the main factor accelerating the aging process. Aging PMMA lenses can cause light-emitting diode (LED) discoloration and distortion. (2) The heat resistance of PMMA material will change with aging. (3) We screened the spectral characteristics of the LEDs and determined the four wavelengths of spectral power as the input characteristics of the LED light color. By introducing the backpropagation (BP) neural network method, a PMMA lens life prediction model was established. The average absolute percentage error of the test set is 4.11%, which indicates that the developed BP neural network has stronger generalizability than the support vector regression and Gaussian process regression models. These findings provide valuable guidance for the design and selection of materials for LED lighting products.