Cooling strategy for LED filament bulb utilizing thermal radiation cooling and open slots enhancing thermal convection

As a novel replacement of conventional light sources, LED filament bulb has gained popularity recently due to its long lifetime, low cost and high energy efficiency. However, the bottleneck in LED filament development is thermal management of the whole bulb and consequential degradation of light output performance. The potential cooling strategies include passive cooling and active cooling. Compared with passive cooling methods, active cooling ones are more costly, space-consuming, heavier and do not apply to the case of filament bulb. Thus, passive cooling such as thermal conductive phosphor-silicon composite and thermal radiation coating wrapped around the filaments can be adopted to boost the thermal conduction and radiation into the environment. Notice that the temperature distribution within phosphor layer is non-uniform, thermal radiation coating can make phosphor temperature more uniform as well as reduce the risk of thermal quenching and hotspot. Here, the effect of our self-developed thermal radiation coatings with different emissivity are compared and investigated. What's more, open slots or holes on the bulb can be considered to enhance the thermal convection of the filament. According to our simulation, the junction temperature will decrease with filament thickness. This is because the outer surface of filament for both thermal convection and radiation is increased, which stimulates the total heat transfer. With this optimized passive cooling strategy, thermal issue of LED filament bulb can be mitigated largely and cost-performance ratio is at a relatively low level.