If both are the same listed Lumens range then the 2 watt could well be using an older technology LED or a less efficient driver circuit. It could also be that one manufacturer is exaggerating output more than the other. If the store will allow it put batteries in both and try them side by side.
If the watts listed are actual battery drain then go for the 1 watt as the batteries will last longer.
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Gear Hubs Owned: Rohloff disc brake, SRAM iM9 disc brake, SRAM P5 freewheel, Sachs Torpedo 3 speed freewheel, NuVinci CVT, Shimano Alfine SG S-501, Sturmey Archer S5-2 Alloy. Other: 83 Colnago Super Record, Univega Via De Oro
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