A lighting unit comprises a packaging substrate (10) formed from a semiconductor, a channel (12) formed in the substrate and a discrete light emitting diode arrangement (34) in the channel. A surface region of the channel comprises doped semiconductor layers (20, 24) which define a light sensor. The arrangement provides a light sensor (which can be used to determine colour and/or output flux) for a LED unit, with the light sensor embedded in substrate used for packaging. This provides a low cost integration process and provides good registration between the light sensor and the LED output.