Study On Angular Color Uniformity Of White LED With Remote Phosphor Structure

Compared with traditional dispensing,remote phosphor coating LED packaging has the advantages of high luminous efficiency and good heat dissipation,which is an important direction of the development of LED lighting.However,remote phosphor coating LED with reflector and air occupies the space between phosphors and LED chips which decrease the extraction efficiency because light was trapped between the reflector,phosphors and LED chips.Besides the mismatch between blue light and yellow light can lead to undesirable angular color uniformity(ACU),a bluish center also known as yellow ring.First,this paper discussed the optical quality of the remote phosphor coating with different angle reflector based on single chip.Simulation results showed that with the decrease of the tilt angle of the reflector,luminous efficiency improved increasingly,but ACU first improved then deteriorated and increased at last.In order to further improve the light quality,a freeform reflector was designed to improve the angular color uniformity of the light source.Simulation results revealed that this reflector can increase the luminous efficiency and greatly improve the ACU.then,the light intensity distribution of the yellow light emitted from phosphor was acquired with the help of optical software.This paper designed a free-form reflector based on the yellow light intensity distribution and edge light principle.Then the corresponding experiments were carried out and the results revealed that compared with the traditional reflector,the application of the free surface reflector improve luminous efficiency from 109 lm/w to 121 lm/w,angular color uniformity improved greatly.but yellow ring also exist.In addition,this paper discussed that different angle of the reflector have an impact on luminous efficiency and ACU,the result showed that with the decrease of the tilt Angle of the reflector,the luminous efficiency increased gradually until the stable state,and the temperature deviation first increased and then decreased.In order to further solve the yellow edge,This papaer placed a diffuser on the phosphor layer,though luminous efficiency decreased 8 lm/w,yellow ring was removed and ACU was further improved.In order to further simplify light source model,This paper put forward the phosphor model of micro-structure,Through simulation it can be seen that with micro-structure of phosphor can improve the ACU,but the luminous efficiency decreased.Compared with the hemispherical microstructure,the pyramidal microstructure can make more light scattering,the color temperature deviation decreased from 1085 K to 77 K,and luminous efficiency fell from 87.5 to 81.4 lm/w because some scattering light is absorbed by reflector and LED chip.And the experiment verify the simulation result.