At the end of life, Metal Halide Lamps exhibit a phenomenon known as “cycling”. These lamps can be started at low voltage but as they heat during operation the internal gas pressure within the arc tube rises and more and more voltage is required to maintain the arc discharge. As a lamp gets older, the maintaining voltage rises to exceed the voltage provided by the electrical ballast. As the lamp heats to this point, the arc fails and the lamp goes out. And eventually, the lamp cools down again, the gas pressure in the arc tube is reduced and the ballast can once again cause the arc to strike. The effect is that the lamp glows for a while and then goes out, repeatedly.