A lighting device 2 suitable for promoting plant growth comprises a first group of LEDs adapted to generate a first emission spectrum having a peak between 450 - 460 nm (royal blue light); a second group of LEDs adapted to generate a second emission spectrum having a peak between 630 - 670 nm (crimson or red light); a third group of LEDs adapted togenerate a third emission spectrum having a peak between 720 - 740 nm (cherry red or far red light) and a fourth group of LEDs adapted to generate white light; wherein the intensity of the light output generated by each group of LEDs is adjustable independently of the other groups. A light fitting comprising multiple such lighting devices is also provided and may include a sensor array 60, such as a CMOS device, which acts as a low resolution camera to measure plant density changes over time. Measures for improving heat transfer from the LEDs using a heat sink in good thermal contact with the main body of a housing of the lighting device (figure 5) and for improving
