I needed a small light to light some steps from my deck to the ground and in a few other places. I already had a 12V system outside.
For a cheap and dirty light I took a plastic test tube (ebay/amazon) put a short section of LED strip light into it (9 leds, served with wires) then heated the open end of the TT with a heat gun, and crimped it with a sheet metal pliers to make a waterproof seal. (the wire insulation melts into the test tube making a hermetic seal) Same system with a dusk to dawn switch can be included with the addition of a photo transistor, a 2N7000 TO-92 size transistor, and a 1-10 meg ohm resistor.
Cheap dirty and pretty rugged too. For mounting, a cable tie with a tab for a screw will work well.
Some of the smaller diameter plastic test tubes will mate to fittings used in 1/2" CPVC plumbing applications. That might make a neat arm for a lamp too; without the melt and crimp step.