Study On Phosphor Particle Sedimentation In High-Power White Led Packaging

Light-emitting diode(LED)has the advantages of energy saving,environmental protection,long service life,small size,which makes LED the fourth generation lighting source.LED has been widely used in general lighting,landscape lighting,display application and other fields.In the packaging process of high-power white LED,the sedimentation of phosphor particles affects the lighting quality and consistency of the LED,which is an important issue in the packaging process.So it's essential to study the phosphor sedimentation systematically.A silicone viscosity model was established at first,then the phosphor sedimentation was studied by means of simulation and experiment.The variation of the silicone viscosity with shear rate,temperature and time was measured by experiment.The results showed that the silicone viscosity remains approximately constant at low shear rate.Therefore,silicone can be considered as Newtonian fluid within a certain range of shear rate.The initial silicone viscosity decreases with the increase of temperature.The viscosity of silicone and growth rate increases with time.Moreover,the silicone viscosity model was built based on the NK model.The comparison between the predicted values in the model and the experimental results verified the accuracy of the model.Taking the change of silicone viscosity into account,Euler two-fluid model was used to simulate the sedimentation of phosphor particles,which focused on the effects of temperature and time on phosphor sedimentation.The results showed that the phosphor sedimentation could be reflected accurately by simulation.Silicone viscosity increases over time,resulting in the increased resistance of phosphor particles.Moreover,the value of the time for the complete sedimentation of phosphor particles and the degree of phosphor particles sedimentation decrease with the increase of temperature.Finally,an online test device was used to study the influence of phosphor sedimentation on LED lighting quality in detail.The results indicated that phosphor particle sedimentation influence the luminous efficiency and CCT significantly.The maximum rate of change of luminous efficiency and CCT is 4.08% and 39.62% respectively.The rise of temperature increases the degree of sedimentation with the temperature lower than 50 °C,while decreases with the temperature higher than 50 °C.