Many times in residential renovation work it is necessary to see into a wall cavity after drilling through the sill or plate. Flashlights put little light into the cavity, block the view through the hole and spill light such that you cannot see anything. For many years I have used the device pictured. This is simply constructed from a discarded wall transformer and a flashlight bulb soldered to the wires. The base of the bulb can be taped up for a strain relief and insulation. This provides safe, transformer-isolated, low-voltage light that can be lowered or pushed up into the wall cavity without obstructing the view through the hole. The wall transformer is the type used for calculators, telephone answering machines, portable radios, etc. The only requirement is that the voltage and current provided by the transformer are close to that of the flashlight bulb selected.