Numerical prediction and experimental validation of multiple phosphor white LED spectrum

Conventional phosphor converted white light LEDs utilize yellow phosphor to convert the blue light emitted from the chip to yellow light. Although this can generate white light with various correlated color temperatures (CCT), the color rendering properties are generally poor as the spectrum of the LEDs, as compared with the reference light source, is not broad enough. The red light output is low in particular. This limitation is caused by the emission spectrum of yellow phosphor. To improve the color rendering properties, multiple phosphors with different emission spectra should be used. For instance, a certain amount of red or orange phosphors may be used to mix with yellow phosphor to increase the output in the red region. In this paper, a numerical model is proposed to predict the emission spectra of LEDs with multiple phosphors. The excitation and emission spectra of various phosphors are measured and input to the model. The mixing ratio and reabsorption between phosphors have also been taken into consideration. White light LEDs with multiple phosphors are fabricated. The spectra are measured and compared with the modeling results. It is found that the proposed model can estimate the emission spectra of LEDs with multiple phosphors with a high degree of accuracy.