The invention relates to embedding data symbols of a data signal into a luminance output of an illumination device. The device includes a controller configured for receiving a first base pattern and a second base pattern within a frame period, and generating a shifted second pattern by phase shifting the second base pattern within the frame period with respect to the first base pattern in response to the data signal such that the data symbols are embedded in the luminance output of the device. The device also includes a first light source configured to generate a first luminance output in response to the first base pattern and a second light source configured to generate a second luminance output in response to the shifted second pattern. The first and second luminance outputs have different output spectra and the luminance output of the illumination device comprises both the first and second luminance outputs. With this approach, the short-time average light output of the illumination device remains constant, decreasing the visible flicker and allowing the use of lower switching frequencies relative to the prior art approaches.