Some people are concerned about whether a 100-watt lamp is sufficient for their plant growth, and if they would need a 250-watt or a 400-watt lamp. The greater the wattage, the higher the brightness. But, will the plant grow faster with the higher wattage? The 2 biggest issues are that the wattage of a lamp is only an indicator of how much electricity the lamp is using (it really doesn't give you any idea of how much light actually hits the plant).
There are basically three elements that can determine a plant's growth; the intensity of the light (PPFD), the amount of time the light is actually available, and the amount of light the plant receives on a daily basis (DLI).
If you have two lights with differing wattages yet both produce the same DLI, the effect on your flora will be identical.
