..For safely discharging the HV Flash capacitors in electronic cameras.
The 4 watt bulbs slowly dissipate the energy of the capacitor.
The bulbs give a positive indication that the cap is discharged when they stop glowing.
Saves screwdrivers and your nerves.

Almost all modern cameras have one of these high energy accumulators.
They are dangerous to you and the camera you are working on.
They retain a charge for several days or weeks and are normally charged
whenever the camera is powered on.

Discharge the capacitor as soon as it is accessable during disassembly.