We use lights extensively during our races (1-5 days duration). We have now settled on a combination of LS type lights. The main light is the Arc LS 2AA. The secondary is a Petzl Zoom modified to take a LS LED. Superb light quality and you can even do fartleg at night on cross country roads (if you so wish!). The last option is a PT Matrix modified to take the Opalec Newbeam module. For use when long life and warning of battery state are required.