## 4 Results and Discussion  
Because human eyes have different relative visual sensitivity for light of different wavelengths, for various SPD (spectral power density), the luminous flux will be the following:  
Figure 4: (**a**) Junction temperature curve (175 mm); (**b**) Junction temperature curve (255 mm); (**c**) The diagram of junction temperature and glue point temperature at stable state (175 mm); (**d**) The diagram of junction temperature and glue point temperature at stable state (255 mm). Figure 3: (**a**) Luminous flux of three CCTs LED filaments after steady state; (**b**) Luminous efficiency of three CCTs LED filaments after steady state. \[\varnothing=K\cdot\int_{380}^{700}\cdot\varnothing(\lambda)V(\lambda)\text{d}\lambda, \tag{1}\]  
where \(K\) is the maximum value of the spectral luminous efficacy, equal to 683 lm/W; \(\varnothing(\lambda)\) is the spectral density of the radiant flux; \(\lambda\) is the wavelength of light; \(V(\lambda)\) is the standard spectral luminous efficacy function specified by the Commission International de I\(\Gamma\)E clearage, which refers to the ratio of two radiation fluxes, \(\lambda_{m}\) and \(\lambda\), at the same wavelength of visual brightness perceived by human eyes under specific photometric conditions. The light efficiency characterizes the ratio of the luminous flux to the electric power consumed. Different sources emit the same luminous flux. The less power consumed, the higher the luminous efficiency. The higher the light efficiency, the better the LED filament's ability to convert electrical energy into light. Two lengths of LED filament were used as the results for analysis. After the filament emits light for 30 min to reach a steady state, the power demands of 2200 K, 2400 K and 2700 K are 4.107 W, 4.056 W and 4.036 W, respectively. It can be seen from Figure 2 that under the same package structure, the luminous efficiency of the 2700 K filament is 111.6 lm/W, which is 35.8 % and 28.9 % higher than that of the 2200 K and 2400 K filaments, respectively. As a comparison group of the 255-mm LED filaments, after reaching a steady state, the powers of 2200 K, 2400 K and 2700 K were 5.886 W, 5.94 W and 5.922 W, respectively. The luminous efficiency of the 2700 K filament is 100.11 lm/W, which is 19.9% and 17.8% higher than that of 2200 K and 2400 K filaments, respectively. In terms of the light efficiency, the 2700 K filament is significantly improved compared to the other two filaments with lower color temperature. According to the conservation of energy, the heat loss of the 2700 K filament is much lower than that of the other two CCT filaments. That is to say, the heat loss of the 2700 K filament is significantly lower than that of the other two filaments. Figure 3 shows the difference in thermal performance of the filament at different color temperatures. As shown in Figure 4a,c, the temperature of the thermocouple glue point of filaments with different color temperatures varies within 0.6 \({}^{\circ}\)C, and the change range is not large. It shows that when the current is constant, the thermocouple glue point temperature has little relationship with the color temperature. As shown in Figure 4d, the thermocouple glue point temperature mainly depends on the material of the thermocouple itself and the passing current. As shown in Figure 4a,b, the junction temperature of the filaments of the two lengths reaches a steady state at about 300 s, and the junction temperature varies greatly. In the steady state, the junction temperature decreases with the increase of the color temperature. In the 175-mm LED filament result, the filament junction temperature decreased by 1.43 \({}^{\circ}\)C (2400 K) and 4.89 \({}^{\circ}\)C (2200 K), respectively. The CCT of the 175-mm LED filament is 2700 K, and the junction temperature is 105.72 \({}^{\circ}\)C in the steady state.