Like these-
http://ns1.bowsite.org/acb/showdetl.cfm?&DID=6&Product_ID=321&CAT ID=8
I like the idea of having more visibility when the arrows heading downrange.
Do tracers like these affect arrow flight at all? What about when they are installed in front of the fletch, like the one seen in the pic? When in front, are they as visible in flight?