I've had sights with the little blue LED that lights up the pins but I have always experienced a "washout" effect in that it makes it hard to see the target due to the light shining. What I've done in the past is to paint the light with a black Sharpie to mute the light. The batteries last quite a while due to the LED but I would recommended only putting it on when needed.

That being said, Tru-Glo puts out a far better product in the form of their Tritium lit pin. The fiber itself glows without the need for any batteries, there is no need to turn it on or off as it says on constantly and has a shelf life of about 10 years I believe....Check it out for yourself!
http://www.truglosights.com/content/products/archery/pins/tfo_pin.asp