Please join hands and read along with me. As strange as it may seem, on page seven of SureFires' Operators Manual, that came with my flash lights, there is a table entitled Lamp Replacement Guide. The guide states that the P60 and P90 lamps should be replaced every hour and that the P61 and P91 should be replaced every 20 minutes. That is the reason I changed my lamp to led for normal use and carry the P60 and P90 for special purposes. The SureFire's Operators Manual is Document #71-01-630 REV 8.