i was thinking the same thing, kirkg. i'm just wondering if there is any mention of this on the package. you would think that a different type of glass is used i'm not sure. this comes to mind with the appliance bulbs for freezers and such too.
It is an extra layer of glass to prevent the glass from shattering from exposure to moisture. Also, the bulb is more sealed to moisture in general. Mostly they are just a little more expensive than interior lights. In terms of lumen performance they are the same.
yeah as already mentioned there is no difference between indoor and outdoor as regards to the wattage or overall light output, the only differences will be in the lamp itself and not the bulb as the outdoor light will have seals and thicker glass.