I have dabbled with arc reactor costuming before, so when I learned of an official licensed arc reactor shirt from Marvel I jumped at the opportunity.  What I got was a good product.  Plenty bright to be seen behind a black shirt.  The arc reactor runs on AAA batteries and is velcro removable for washing the shirt. I bought mine from ThinkGeek for $30. The only problem I found with the shirt was the shirt itself.  The arc reactor is not heavy but is enough that it pulls down the collar of the shirt, making it sit awkward on your chest.  In addition, the shirt wasn’t comfortable.  I wear a large, so I ordered a…