Think of the bulb like a rubber hose; voltage is pressure, current (amps) is the amount of water flow, and power (watts) is the amount of energy in the water flowing through the hose to turn a waterwheel (pressure x flow = power). The hose is designed to carry a certain amount of water flow at a certain pressue, if you increase the pressure a little, the flow will increase and the water will contain more energy; if you increase the pressure too much, the hose will burst. How much extra pressure you can get away with depends on the design and quality of the hose.