It should not respond when a caplamp is shone at it. Not adversely affected by ambient light Cavers will usually be operating the slave unit in the dark, so the question of ambient light does not arise. However, if you want to operate it in conditions where there is some light you need to know how its performance is affected. The response has been tailored to work in ambient light as a fill-in flash. The unit is designed to be triggered by the sharp pulse from an electronic flashgun, and to ignore the much slower changes in light level caused by a wavering caplamp beam.
Flashbulbs come somewhere in between.
As it stands, the unit can be triggered by a flashbulb. The unit is perfectly capable of triggering a bulb flashgun, but there are some points to note, as discussed in my pamphlet. The unit fits inside a translucent container roughly the size of a 35mm film container. It could, perhaps, be placed inside the casing of a flashgun, and operated from the flashgun's own batteries. On the left is the battery holder.