What is the basic principle of a television picture tube or fluorescent light tubes ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Fluorescence:**
- Fluorescence is a process where a substance absorbs electromagnetic radiation (light) and then re-emits it almost instantaneously. This is the fundamental principle behind both television picture tubes and fluorescent light tubes.

2. **Principle of Television Picture Tube:**
- A television picture tube, also known as a cathode ray tube (CRT), operates on the principle of fluorescence. In a CRT, electrons are emitted from a cathode and accelerated towards a phosphorescent screen.
- When these high-speed electrons strike the screen, they excite the phosphorescent material, causing it to emit visible light. This process creates the images we see on the television screen.
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