Lights

Buck driver is only 4 parts: Coil, capacitor, Schottky diode, transistor. Easily made boardless.

I consider the time spend replacing burnt out LEDs to be more costly than getting it right in the first place, also a Buck would waste a lot less energy than a resistor. The limiting factor in Buck efficiency is how fast a schottky you can afford.

-still using the alkaline batteries and LEDs as fitted last October, so no problems with blown components or battery life (yet)

I'm sure you're right - I don't remember Buck drivers being on the syllabus when I stopped teaching - I was more floating the possibility of retro fitting a bit of this century to a bit of the last, and used what I had to hand.

Just out of curiosity, will a Buck driver cope with a change in supply voltage? I'm thinking of alkaline batteries running down over time and also the possibility of replacing alkaline cells with NiMH.