Puck lights are small battery powered LED lights, usually with five LED’s, usually used for quick installation in closets, under kitchen counters, etc.  I assume the name comes from the fact that they look a bit like a hockey puck.  They are a very useful lighting option for board slotting machines- Mindy Dubansky from the Met, investigated lighting for her slotting machine, and a lighting expert suggested this solution.  It is a bit counterintuitive, lighting from below to see the board edge on the top of the blade, but in practice it works great.