Fig. 1. Emission spectrum of LED bulbs and photograph of LED light source module

Fig. 2. Luminous flux maintenance of LED bulbs under different currents at room temperature

Fig. 3. Performances of LED bulbs versus aging time under different currents at room temperature. (a) Chromaticity coordinates; (b) color temperature; (c) color rendering index; (d) emission intensity ratio between yellow phosphor and blue chip

Fig. 4. Aging effects of light source module of LED bulbs under different currents at room temperature. (a) Appearance; (b) infrared thermal imaging; (c) substrate of driving power

Fig. 5. I-V characteristics of chips aged under different currents at room temperature

Fig. 6. Characteristics of LED bulbs under different currents at 55 ℃. (a) Luminous flux maintenance; (b) chromaticity coordinates; (c) color temperature; (d) color rendering index

Fig. 7. Effect of joint temperature-current stress on characteristic of LED bulbs. (a) Emission intensity ratio between yellow phosphor and blue chip; (b) I-V curves of chips and substrate of driving power

Fig. 8. Effect of joint temperature-current stress on characteristics of LED bulbs at 55 ℃ temperature. (a) Aging photographs of light source modules and spectral changes; (b) infrared thermal distributions of light source modules