A method comprising: measuring a first color of light emitted from an assembled LED based illumination device that includes an amount of a first wavelength converting material and an amount of a second wavelength converting material ; determining a material modification plan based at least in part on the first color of light that includes a modification of the amount of the first wavelength converting material and a modification of the amount of the second wavelength converting material, wherein the assembled LED based illumination device , modified in accordance with the material modification plan, emits a second color of light within a predetermined tolerance of a target color point, and determining the material modification plan further includes determining locations for the modification of the amount of the first wavelength converting material and the amount of the second wavelength converting material based on a performance metric for the assembled LED based illumination device that is in addition to the target color point, wherein the performance metric for the assembled LED based illumination device comprises any of a color conversion efficiency of the assembled LED based illumination device , a color uniformity of the assembled LED based illumination device , and a temperature distribution over a light emitting surface of the assembled LED based illumination device ; and modifying the amount of the first wavelength converting material and the amount of the second wavelength converting material of the assembled LED based illumination device in accordance with the material modification plan. measuring a first color of light emitted from an assembled LED based illumination device that includes an amount of a first wavelength converting material and an amount of a second wavelength converting material ; determining a material modification plan based at least in part on the first color of light that includes a modification of the amount of the first wavelength converting material and a modification of the amount of the second wavelength converting material, wherein the assembled LED based illumination device , modified in accordance with the material modification plan, emits a second color of light within a predetermined tolerance of a target color point, and determining the material modification plan further includes determining locations for the modification of the amount of the first wavelength converting material and the amount of the second wavelength converting material based on a performance metric for the assembled LED based illumination device that is in addition to the target color point, wherein the performance metric for the assembled LED based illumination device comprises any of a color conversion efficiency of the assembled LED based illumination device , a color uniformity of the assembled LED based illumination device , and a temperature distribution over a light emitting surface of the assembled LED based illumination device ; and modifying the amount of the first wavelength converting material and the amount of the second wavelength converting material of the assembled LED based illumination device in accordance with the material modification plan. <EOS>