AL O Hi Dave, The UV light is most likely going to be from the manufacture. Other than the battery replacement there are no external screw for easy disassembly. It is designed to purify either a pint (1/8th of a gallon) or a quart (1/4) of a gallon. The "8000" spec is probably for a pint meaning it should do 1000 gallons. I have no idea how much the UV light costs. I used a pump water filter for 27 years and it still works fine. I had to disassemble it to dry it out after each trip. After each season I put the filter cartridge in a glass filled with bleach and let it soak over night. If I recall correctly I bought only 1 replacement filter. I bought this pen because I'm 51 years old and can't hike with the endurance I use to. The difference is a quarter to a half a pound less weight. The pen takes longer than the pump to get water. Mosquitoes tend to swarm around water holes. The other difference is I can drop the pump hose into a vary small spot of water and suck it up. Hope this helps. Al