For the wattage of LED lights, actually it is a common sense in this industry to name the chips 3w or 5w or 10w based on its size, not the real wattage. For example. a 5w chips, is not real 5w, but 2.3~2.5w usually.
And led is not like HPS or HID, the more wattage the better, it actually has a maximum brightness wattage, when it reaches the highest brightness, no matter it is 2.3 or 2.5w, the light won't change on its brightness, so it would be better to use the lower wattage, to save electricity also help lengthen the life span of the chips.
Also, the real wattage of the lights has something to do with the efficiency of the power supply, the higher efficiency of the power supply is, the wattage of the lights will be lower, on the contract, if the power supply has low efficiency, then, the wattage will also be higher. Hope this also helps in some degree.