Spectral coherence of white LEDs

Abstract

We address space–frequency domain coherence properties of broadband light-emitting diodes (white LEDs) and fields radiated by them. Inverse-source techniques are employed to determine the spectral degree of spatial coherence of an effective planar source representing a real LED, and coherent elementary fields associated with it. By fitting with experimental measurements, we formulate simple analytical coherence models that can be used as a basis for theoretical and experimental studies of the coherence of polychromatic stationary light in free space and in various optical systems. In particular, we find that radiation from white LEDs follows closely Wolf’s scaling law for spectral invariance [Phys. Rev. Lett. 56, 1370 (1986)PRLTAO0031-900710.1103/PhysRevLett.56.1370] in the blue and the phosphor-generated parts of the spectrum separately, but not across the entire white-light spectrum.