In the 2005 Surefire Illumination catalog, the L4 is listed at 65 lumens. In the 2006 catalog it is now listed as 100 lumens. The L5 is larger and will be receiving an LED upgrade this year. It is roughly the same size as the 6P, but the grip ring makes it difficult if not impossible to reuse the same holsters, unless you have one of Surefire's speed holsters. The L4 on the other hand, is much slimmer than the 6P but still a durable light.