According to a first aspect of the invention, there is provided an illumination device (100) comprising: a light source (102) configured to emit light of a first wavelength; a wavelength converting layer (104) comprising a wavelength converting material configured to receive light from the light source, and further configured to convert light from the first wavelength to a second wavelength; a periodic plasmonic antenna array, arranged embedded within the wavelength converting layer, and comprising a plurality of individual antenna elements (108) arranged in an antenna array plane, the plasmonic antenna array being configured to support a first mode of surface lattice resonances at the second wavelength, arising from diffractive coupling of localized surface plasmon resonances in the individual antenna elements, wherein the plasmonic antenna array is configured to comprise plasmon resonance modes such that light emitted from the plasmonic antenna array has an anisotropic angle distribution; and wherein the light source is further arranged to emit light in the form of a plane wave (103) having an angle of incidence in relation to the antenna array plane such that an electric field intensity in the antenna elements, resulting from the said plasmonic-photonic lattice resonances, is minimized.