Exactly what I did and have been using for 2 years (here's my write-up) - they definately throw some light down the road
the 4509 only has a 25hr life, there is a number of company's doing LED. But that goes out of "inexpensive". Look for PAR36 lights. 500 lumens
http://www.stolztelecom.com/p36slc-par-36-12-24-vdc-replacement.html
http://www.aircraftspruce.com/catalog/elpages/whelenpar362.php
http://www.aircraftspruce.com/catalog/elpages/whelenpar363.php
http://www.whelen.com/_AUTOMOTIVE/details_prod.php?head_id=12&cat_id=74&prod_id=469#
video from Whelen
http://www.whelen.com/_AVIATION/media/parmetheus/parmetheus.html