Adding a separate switch outside the lighthouse or gadget allows you to turn the bulb on and off without having to touch the torch itself. If you have made a lighthouse then this can be a lot of fun because you can design your own flashing light sequences just like in a real lighthouse.
You can even send messages by Morse Code.
Morse Code was a very important way to send messages before telephones were invented in 1876. Long after this time it is still being used for communications at sea, in emergencies and in some countries of the world.
Morse code is a simple sequence of short and long flashes (or bleeps of a buzzer) written as dots and dashes. Each combination of flashes stands for a letter of the alphabet.
For example . . . _ _ _ . . .
means S O S
In other words if you made your lighthouse flash as follows
3 short flashes then 3 long flashes then 3 short flashes you will have sent the message SOS.
You could also spell out your name in flashes of light!
You can see a complete copy of the Morse Code Alphabet in the Science Investigations section on the page with title Electricity 1.