Lighting systems

An LED light unit 5 is provided with terminal pins 11 at each end for fitting the light unit 5 in place of a fluorescent tube of a fluorescent lighting fixture connected to a power source. The light unit 5 has a circuit board 9 with a plurality of diodes 15a configured to provide at least one string of visible light producing LEDs and at least one string of zener diodes. The strings are driven by drive means 17 whereby a constant input operating voltage to the light unit 5 is provided when the light unit is used with a ballast and the power derived is dissipated in any one or more of the strings.