Efficient color mixing through etendue conservation using freeform optics

Simone Sorgato, Ruben Mohedano, Julio Chaves, Aleksandra Cvetkovic, Maikel Hernandez, Pablo Benitez, Jc Minano, Hugo Thienpont, Fabian Duerr

Research output: Chapter in Book/Report/Conference proceedingConference paper

2 Citations (Scopus)


Today's SSL illumination market shows a clear trend towards high flux packages with higher efficiency and higher Color Rendering Index, realized by means of multiple color chips and phosphors. Such light sources require the optics to provide both near- and far-field color mixing. This design problem is particularly challenging for collimated luminaries, since traditional diffusers cannot be employed without enlarging the exit aperture and reducing brightness. Furthermore, diffusers compromise the light output ratio (efficiency) of the lamps to which they are applied.

A solution, based on Khler integration, consisting of a spherical cap comprising spherical microlenses on both its interior and exterior sides was presented in 2012. The diameter of this so-called Shell-Mixer was 3 times that of the chiparray footprint. This work shows a new version of the Shell-Mixer, based on the Edge Ray Principle and conservation of etendue, where neither the overall shape of the optic nor the surfaces of the lenses are constrained to spheres or rotational Cartesian ovals. The new shell is freeform, only twice as large as the chip-array footprint and equals the original model in terms of color uniformity, brightness and efficiency.
Original languageEnglish
Title of host publicationNonimaging optics: efficient design for illumination and solar concentration XII
Number of pages8
ISBN (Print)978-1-62841-738-8
Publication statusPublished - 2015
EventEfficient Design for Illumination and Solar Concentration XII - , United Kingdom
Duration: 9 Aug 201510 Aug 2015


ConferenceEfficient Design for Illumination and Solar Concentration XII
Country/TerritoryUnited Kingdom


  • LEDs
  • Color Mixing;
  • Freeform
  • Kohler integration;
  • Etendue
  • Illumination


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