The most likely cause of an MV bulb cycling on and off is a failing ballast. MV bulbs are designed to operate with a specific voltage and current, and the ballast provides the necessary voltage and current regulation. If the ballast is failing, it may not be able to provide the correct voltage and current to the bulb, which can cause the bulb to cycle on and off.Another possibility is that the bulb itself is failing. As an MV bulb ages, it will gradually lose its ability to produce light. This can cause the bulb to become dimmer and eventually fail completely. However, it is less likely that a 5-6 year old MV bulb would be failing already.To determine which component is failing, you can try replacing the bulb first. If the new bulb does not cycle on and off, then the problem is most likely the ballast. If the new bulb also cycles on and off, then the problem is most likely the bulb itself. Flag for review