What You Did
You simulated a fiber optic cable with a stream of water.
When you removed the tape, some of the light bent as it followed the stream of water out of the bottle rather than shining straight through it as normal.Making the hole bigger makes more of the light bend as more photons get caught in the stream of water.
Using a weak flashlight will make for a less brilliant effect.
Try making the hole even bigger. Compare different colors of light
fiber optics, electromagnetism, communication systems