Place a candle in a dark room. When it sucks all the dark it can hold, it goes out. The dark is stronger. The evidence that the candle was sucking dark is that the wick, once white, turns black. All the dark sucked in left its mark.
Light bulbs operate in the same way.
Once they suck all the dark they can hold, they go out. You can see the dark spot left on the bulb as proof that it's full. Larger dark suckers in parking lights, or massive ones in stadiums have a much greater capacity, but once full they leave large dark spots as evidence of the superior strength of darkness. Dark is heavier than light. It has mass.