Which of the following statements is true about LEDs?
- A
High operational voltage
- B
Warm-up time is required
- C
Bandwidth of light is $4000\mathop {\rm{A}}\limits^{\rm{o}}-7000 \mathop {\rm{A}}\limits^{\rm{o}}$
- D
Fast on-off switching
✓ Correct answer: D
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