Final answer:
The output phosphor of an image intensifier tube converts the electronic image into a visible light image.
Step-by-step explanation:
The output phosphor of an image intensifier tube serves to convert the electronic image into a visible light image.
When the accelerated electrons strike the phosphor coating on the output screen of the image intensifier tube, they cause the phosphor to emit visible light. This visible light forms the image that is viewed by the observer.
Therefore, the correct answer is option 3 - visible light image.