Why does Fluorescent bulb not light and end turns black?

In order to know why fluorescent bulbs turn black at the end, you need to understand how they work. Basically, when you turn on the lighht switch, the ballast sends a spark through the Mercury-vapor-filled tube or bulb, depending on design. When it does this, it creates light by activating phosphors that coat the inside of the tube.

Well each time the ballast fires, it creates emissions. These emissins materials then settle on the surface inside the glass. After awhile this material piles up. When it does this, the tube end turns completely black. Not only does the tube end turn black, but the accumulated materials pile up so high that it blocks the electrons that flow into the mercury. When this happens, you will notice the bulb or tube flicker heavily and then burn out.