Hi, I am new to landscape lighting. Just getting started. I purchased the kit with the transformer and 9 lights from Costco. I see the Costco version of the transformer has only 15v. The bulbs seem rated for 11-18v so I believe I should be ok. I was thinking of purchasing more lights. Does overvolting reduce the life of the bulbs? Was kind of surprised there is no 12V option on the transformer since the version on the Volt website does seem to have it.