I’ve been playing around with LED lighting for years now, getting hold of non-working flash lights, removing the LED’s and using them in a variety of applications. The most common application has been with motion-sensing night-lights. I remove the incandescent bulb and replace it with several LED’s inside a reflctor. I also use NiCad or lithium batteries as the power source.
These days, one can buy LED motion-sensing night-lights, but these use conventional alkaline batteries, such as the Globe LED Motion Activated Locker Light. The cheapest I’ve seen so far are sold at CVS pharmacy for about $7.50. What I do with these lights is that I remove all of the connectors for the batteries, cut out a slot in the top of the battery compartment, and place a couple of flat strips to connect a lithium battery whose dimension is around 47 x 33 x 8 mm. This replaces the three AAA batteries and lasts a lot longer.
Another use I’ve had with LED’s is with the 110v screw-in light bulb replacement. However, these seem to be rather unreliable due to thermal runaway as each LED is wired in series without any current limiter. I’ve actually broken down some of these and re-built them using a plastic funnel and old screw bases. Using my own bridge rectifier and smoothing capacitor helps a little as well as placing two bulbs in series yielding some 60 LED’s is better than a single light with 30 LED’s, a limiting capacitor in series and no smoothing electrolytic capacitor. It’s easy to use two bulbs in series within a couple of hurricane lights that normally use two conventional incandescent lights. This setup uses just over 4 watts of power per lamp, instead of some 60 watts, or 25 watts using florescent lights.
I’ve also placed 5 sets of LED lights within a low level outside wall with each set comprising 4 LED’s in series triggered by a motion sensor and a 12-volt line that is solar powered.
Here's an interesting site that shows how to replace the lithium batteries in a laptop battery pack, something I've done several times.
I've always had an interest in steam locomotives, here is GWR 6024 at Abergavenny.