## 1 Introduction  
Light-emitting diodes (LED), an ultramodern cold light source, have the advantages of energy saving, environmental protection, long life and stable performance. Therefore, it is widely used in daily lighting, animal and plant culture and even liquid crystal display [1, 2, 3, 4]. However, when using LEDs as everyday lighting materials, there are many aspects to pay attention to. Efficiency and color characteristics must be considered when designing LED light sources [5, 6]. The color of the light emitted by the LED filament is not exactly the same as the color of the light emitted by the black body at various temperatures, so the concept of \"correlated color temperature\" is used in LED. [PERSON] et al. concluded that 80% of the energy input to the LED is dissipated as heat [7]. Therefore, the key to LED development is how to process heat management efficiently.  
LED filament is the core component of LED light bulb. Different packaging methods, packaging substrate materials, phosphor ratio, chip size and substrate have a crucial impact on the optical properties and heat dissipation of LED filaments [8, 9, 10, 11]. Ref. [12] conducted experimental and numerical analyses of LED modules using aluminum substrates and anisotropic graphite composites with a stationary heat source and ratio of length to diameter of substrate. The lateral temperature distribution of graphite substrate is more uniform under the same input power. Meanwhile, they concluded that the thermal conductivity of substrate has a great influence on high power LED. [PERSON] et al. designed a compact and high-power LED arrays considering the packaging methods, thermal interface materials and electrical tracer layer, which significantly reduces the temperatures and effectively extends the service life [13]. [PERSON] et al. studied thermal performance experiments on LED steam chamber substrate, copper substrate and aluminum substrate. When the input power is fixed at 6 W, the experimental thermal resistance values of copper substrate and steam chamber substrate are 0.41 \({}^{\circ}\)C/W and 0.38 \({}^{\circ}\)C/W, respectively. The optical power of steam chamber substrate is 5% greater than that of aluminum substrate [14]. [PERSON] et al. conducted the effect of the thermal resistance inflection point of dual chips caused by the thermal boundary on the PN junction temperature [15]. The larger the distance between the plate and the edge, the higher the temperature of the PN junction, and the greater the influence on heat dissipation. This conclusion is consistent in different current magnitudes. However, few teams of researchers have conducted a series of theoretical studies that directly correlate CCT with the thermal properties of LED filaments through phosphors.  
Electric energy is not only converted into heat energy, but also more than 20% of the energy is converted into light in the LED filament [16; 17]. Therefore, the photoelectric performance should also be considered as an important factor when studying the influence of color temperature on the thermal performance of LED filament structure.  
The purpose of this paper is to study the influence of color temperature on the thermal properties of LED filaments. Through the experimental measurement of LED filaments with the same substrate, chip and package structure but different color temperature, the relationship between color temperature and the thermal performance of LED filaments is studied by utilizing light efficiency, light flux, the junction temperature and thermal resistance.