Perhaps you are like me and need to run a UV light for insects even when it rains, or especially when it rains (think rain beetles). I have chewed through a bunch of the off the shelf UV lights over the years because they are not made to get wet. Neither the ballast nor the photoelectric switch from BioQuip is designed to be exposed to rain. Plastic bags and duct tape can only do so much.
Given my need for a ‘rain or shine light,’ I looked at the kind of materials used in off-road vehicles, marine applications and home, 12 volt solar systems to see what was being used to run lights that must stand up to the elements day in and day out.
The system I built has a number of advantages over the pre-made systems; 1. minimum 16 gauge wire for better flow of current and less heat, 2. fully sealed aluminum circuit box protects the ballast from water and acts as a heat sink, 3. in-line fuse protects ballast from over amping, 4. the marine-grade photoelectric switch is completely weather proof.
The cost of materials is very similar to the pre-made systems, with the DIY one a bit cheaper ($115 v. $134).
The BioQuip light + switch system is smaller and lighter. If you need light weight for a long hike then this is not the design for that. If you use cheaper materials you can make a very basic fair weather light cheaper still, but you get what you pay for. There is the advantage that when you buy a system you don’t spend the time and effort to build it and if it fails you might be able to return it for repair or replacement (But not if you leave it out in the rain. Remember “protect from dampness.”)
But if you like to DIY then here is some more information that can help you see how I built mine.